Communication method and apparatus in full-dimensional multiple-input multiple-output mobile communication system

ABSTRACT

A method for transmitting and receiving channel state information at a terminal of a mobile communication system according to an embodiment of the preset specification comprises the steps of: determining at least one of first precoding information and first rank information corresponding to a first dimension; receiving, from a base station, a reference signal corresponding to a second dimension; determining at least one of second precoding information and second rank information corresponding to the second dimension, on the basis of the reference signal; and transmitting, to the base station, channel state information which has been determined on the basis of at least one of the first precoding information, the first rank information, the second precoding information and the second rank information. According to an embodiment of the present specification, it is possible to correctly transmit and receive pre-coding information and channel state information at a terminal and a base station including a plurality of antennas, and to reduce an overhead occurring at the time of transmission and reception.

TECHNICAL FIELD

The present disclosure relates to a wireless mobile communicationsystem, and more particularly, to a method of transmitting and receivinga PMI and channel status information, through which a User Equipment(UE) measures a channel quality (radio channel status) to operate as aHybrid MEMO system, and report the same to an evolved Node B (eNB) inthe wireless mobile communication system to which a multi-access schemeusing multiple carriers, such as Orthogonal Frequency Division MultipleAccess (OFDMA) or the like, is applied.

BACKGROUND ART

From the early stage of providing voice-oriented services, a mobilecommunication system has evolved into a high-speed, high-qualitywireless packet data communication system to provide data and multimediaservices. To this end, various standardization organizations such as3GPP, 3GPP2, IEEE, and the like have been working on the standardizationof the 3rd evolved mobile communication system to which a multi-accessscheme that uses multiple carriers is applied.

Recently, various mobile communication standards such as Long TermEvolution (LTE) of 3GPP, Ultra Mobile Broadband (UMB) of 3GPP2, 802.16mof IEEE, and the like have been developed to support a high-speed andhigh-quality wireless packet data communication system based on themulti-access scheme using multiple carriers.

The currently existing 3rd evolved mobile communication system, such as,LTE, UMB, 802.16m, and the like, is based on the multi-carriermulti-access scheme. To improve the transmission efficiency, the systemapplies Multiple Input Multiple Output (MEMO (multiple antennas)), anduses various technologies, such as beam-forming, Adaptive Modulation andCoding (AMC), channel sensitive scheduling, and the like. The varioustechnologies may enhance the transmission efficiency and improve thesystem throughput through a method of concentrating a transmission powerthat is transmitted from multiple antennas or adjusting an amount oftransmitted data based on a channel quality or the like, and selectivelytransmitting data to a user having a good channel quality, or the like.Most of those schemes are operated based on channel status informationof a channel between an eNB (or Base Station (BS)) and a UE (or a MobileStation (MS)) and thus, the eNB or the UE may need to measure a channelstatus between the eNB and the UE. In this instance, Channel statusindication reference signal (CSI-RS) is used. Then eNB mentioned aboverefers to a downlink transmission and uplink reception device located ata predetermined place, and one eNB can perform transmission or receptionfor multiple cells. In a single mobile communication system, a pluralityof eNBs are geographically distributed and each eNB performstransmission and reception for a plurality of cells.

The existing 3rd and 4th mobile communication system, such as, LTE,LTE-A, or the like, utilizes the MIMO technology that executestransmission using a plurality of transmitting and receiving antennas toimprove the data transmission rate and the system throughput. Generally,the number of information streams to which spatial multiplexing is to beapplied may vary based on the number of antennas included in atransmitter and a receiver. Generally, the number of information streamsto which spatial multiplexing can be applied is referred to as a rank ofa corresponding transmission. In the case of the MIMO technologysupported in the standards up to LTE/LTE-A Release 11, spatialmultiplexing with respect to the case in which the number oftransmission antennas and the number of reception antennas arerespectively 8, is supported, and a rank is supported up to 8. Incontrast, the FD-MIMO system, which has been evolved from the existingLTE/LTE-A MIMO technology, may use 32 or more transmission antennas,which are more than 8 transmission antennas. Such an FD-MIMO system asdescribed above requires a method and an apparatus for transferring thechannel state.

DESCRIPTION OF THE INVENTION Technical Problem

Embodiments of the present disclosure are to provide a method and anapparatus for measuring a reference signal, generating channel stateinformation, and transmitting channel state information by a UE for ahybrid MIMO of a new concept having advantages of both an open-loop MIMOand a closed-loop MIMO in an FD-MIMO transmission and reception.Further, embodiments of the present disclosure are to provide a methodand an apparatus for, by an eNB, transmitting a reference signal to a UEand receiving channel state information transmitted by the UE.

Solution to Problem

A method for transmitting and receiving channel state information by aUE of a mobile communication system according to an embodiment of thepresent disclosure includes: determining at least one of first precodinginformation and first rank information corresponding to a firstdimension; receiving a reference signal corresponding to a seconddimension from an evolved Node B (eNB); determining at least one ofsecond precoding information and second rank information correspondingto the second dimension, on the basis of the reference signal; andtransmitting, to the eNB, channel state information which has beendetermined on the basis of the at least one of the first precodinginformation, the first rank information, the second precodinginformation, and the second rank information.

A method for transmitting and receiving channel state information by aneNB of a mobile communication system according to another embodiment ofthe present disclosure includes: identifying at least one of firstprecoding information and first rank information corresponding to afirst dimension; transmitting, to a UE, a reference signal correspondingto a second dimension; and receiving, from the UE, channel stateinformation which has been determined on the basis of at least one ofthe first precoding information, the first rank information, secondprecoding information, and second rank information, wherein at least oneof the second precoding information and the second rank informationcorresponding to the second dimension is determined on the basis of thereference signal.

A UE for transmitting and receiving channel state information in amobile communication system according to another embodiment of thepresent disclosure includes: a transmission/reception unit configured totransmit and receive a signal; and a controller configured to controlthe transmission/reception unit, determine at least one of firstprecoding information and first rank information corresponding to afirst dimension, receive, from an eNB, a reference signal correspondingto a second dimension, determine at least one of second precodinginformation and second rank information corresponding to the seconddimension, on the basis of the reference signal, and transmit, to theeNB, channel state information which has been determined on the basis ofat least one of the first precoding information, the first rankinformation, the second precoding information, and the second rankinformation.

An eNB for transmitting and receiving channel state information in amobile communication system according to another embodiment of thepresent disclosure includes: a transmission/reception unit configured totransmit and receive a signal; and a controller configured to controlthe transmission/reception unit, identify at least one of firstprecoding information and first rank information corresponding to afirst dimension, transmit, to a UE, a reference signal corresponding toa second dimension, and receive, from the UE, channel state informationwhich has been determined on the basis of at least one of the firstprecoding information, the first rank information, second precodinginformation, and second rank information, wherein at least one of thesecond precoding information and the second rank informationcorresponding to the second dimension is determined on the basis of thereference signal.

Advantageous Effects of Invention

Embodiments of the present disclosure enable exact transmission andreception of precoding information and channel state information by a UEor an eNB including a plurality of antennas and can reduce the overheadgenerated during the transmission or reception.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an FD-MIMO system according to an embodiment of thepresent disclosure;

FIG. 2 illustrates a wireless resource of one subframe and one resourceblock (RB) in an LTE/LTE-A system;

FIGS. 3A and 3B illustrate a method of transmitting a CSI-RS accordingto an embodiment;

FIG. 4 illustrates a UE which transmits RI, PMI, and CQI for a2D-CSI-RS;

FIG. 5 illustrates a UE, which transmits a RI, PMI, and CQI with respectto a plurality of CSI-RSs;

FIG. 6 illustrates precoding corresponding to a PMI_(H) according to anembodiment, which is allocated to an open-loop MIMO and is definedaccording to time and frequency resources;

FIG. 7 illustrates precoding corresponding to PMI_(H) according to anembodiment, which is allocated to an open-loop MIMO and is definedaccording to time and frequency resources;

FIG. 8 illustrates a UE, which transfers an RI_(V) and a PMI_(V) to aneNB according to method 1 for defining a precoding set according to aresource, according to an embodiment;

FIG. 9 illustrates a UE, which transfers an RIV and a PMI_(V) to an eNB,using method 2 for defining a precoding set according to a resourcedepending on an embodiment;

FIG. 10 illustrates an example of an assumption of method 1 for definingprecoding for each subband by an eNB and two UEs according to anembodiment;

FIG. 11 illustrates an example of an assumption of method 2 for defininga precoding for each subband by an eNB and two UEs according to anembodiment;

FIG. 12 illustrates an example of an assumption of method 3 for defininga precoding for each subband by an eNB and two UEs according to anembodiment;

FIG. 13 illustrates an example of an assumption of method 4 for defininga precoding for each subband by an eNB and two UEs according to anembodiment;

FIG. 14 illustrates an example of pre-defining time and frequencyresources for defining a plurality of precoding sets {PMI_(H), PMI_(V)},using method 5 for defining a precoding by a subband according to anembodiment;

FIG. 15 illustrates a method for pre-defining a PMI_(H) for each timeand frequency resource, according to method 1 for defining a precodingby a wideband to each UE according to an embodiment;

FIG. 16 illustrates a method for pre-defining a PMI_(V) for each timeand frequency resource, according to method 2 for defining a precodingby a wideband to each UE according to an embodiment;

FIG. 18 illustrates a method for pre-defining a PMI_(V) and a PMI_(H)for each UE, according to method 4 for defining a precoding by awideband to each UE according to an embodiment;

FIG. 19 illustrates an example of pre-defining time and frequencyresources for defining a plurality of precoding sets {PMI_(H), PMI_(V)},using method 5 for defining a precoding by a wideband according to anembodiment;

FIG. 20 illustrates an operation of an eNB using method 1 for definingone precoding according to a resource, according to an embodiment of thepresent disclosure;

FIG. 21 illustrates an operation of a UE using method 1 for defining oneprecoding according to a resource, according to an embodiment of thepresent disclosure;

FIG. 22 illustrates an operation of an eNB using method 2 for definingone precoding according to a resource, according to an embodiment of thepresent disclosure;

FIG. 23 illustrates an operation of a UE using method 2 for defining oneprecoding according to a resource, according to an embodiment of thepresent disclosure;

FIG. 24 illustrates an operation of an eNB using method 1 for defining aprecoding set according to a resource, according to an embodiment of thepresent disclosure;

FIG. 25 illustrates an operation of a UE using method 1 for defining aprecoding set according to a resource, according to an embodiment of thepresent disclosure;

FIG. 26 illustrates an operation of an eNB using method 2 for defining aprecoding set according to a resource, according to an embodiment of thepresent disclosure;

FIG. 27 illustrates an operation of a UE using method 2 for defining aprecoding set according to a resource, according to an embodiment of thepresent disclosure;

FIG. 28 illustrates an equipment drawing of an eNB in a FD-MIMO system,according to an embodiment of the present disclosure; and

FIG. 29 illustrates an equipment drawing of a UE in a FD-MIMO system,according to an embodiment of the present disclosure.

MODE FOR THE INVENTION

Hereinafter, embodiments of the present disclosure will be described indetail with reference to the accompanying drawings.

In describing the exemplary embodiments of the present disclosure,descriptions related to technical contents which are well-known in theart to which the present disclosure pertains, and are not directlyassociated with the present disclosure, will be omitted. Such anomission of unnecessary descriptions is intended to prevent obscuring ofthe main idea of the present disclosure and more clearly transfer themain idea.

For the same reason, in the accompanying drawings, some elements may beexaggerated, omitted, or schematically illustrated. Further, the size ofeach element does not entirely reflect the actual size. In the drawings,identical or corresponding elements are provided with identicalreference numerals.

The advantages and features of the present disclosure and ways toachieve them will be apparent by making reference to embodiments asdescribed below in detail in conjunction with the accompanying drawings.However, the present disclosure is not limited to the embodiments setforth below, but may be implemented in various different forms. Thefollowing embodiments are provided only to completely disclose thepresent disclosure and inform those skilled in the art of the scope ofthe present disclosure, and the present disclosure is defined only bythe scope of the appended claims. Throughout the specification, the sameor like reference numerals designate the same or like elements.

Here, it will be understood that each block of the flowchartillustrations, and combinations of blocks in the flowchartillustrations, can be implemented by computer program instructions.These computer program instructions can be provided to a processor of ageneral purpose computer, special purpose computer, or otherprogrammable data processing apparatus to produce a machine, such thatthe instructions, which execute via the processor of the computer orother programmable data processing apparatus, create means forimplementing the functions specified in the flowchart block or blocks.These computer program instructions may also be stored in a computerusable or computer-readable memory that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer usable orcomputer-readable memory produce an article of manufacture includinginstruction means that implement the function specified in the flowchartblock or blocks. The computer program instructions may also be loadedonto a computer or other programmable data processing apparatus to causea series of operational steps to be performed on the computer or otherprogrammable apparatus to produce a computer implemented process suchthat the instructions that execute on the computer or other programmableapparatus provide steps for implementing the functions specified in theflowchart block or blocks.

And each block of the flowchart illustrations may represent a module,segment, or portion of code, which includes one or more executableinstructions for implementing the specified logical function(s). Itshould also be noted that in some alternative implementations, thefunctions noted in the blocks may occur out of the order. For example,two blocks shown in succession may in fact be executed substantiallyconcurrently or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved.

As used herein, the “unit” or “module” refers to a software element or ahardware element, such as a Field Programmable Gate Array (FPGA) or anApplication Specific Integrated Circuit (ASIC), which performs apredetermined function. However, the “unit” or “module” does not alwayshave a meaning limited to software or hardware. The “unit” or “module”may be constructed either to be stored in an addressable storage mediumor to execute one or more processors. Therefore, the “unit” or “module”includes, for example, software elements, object-oriented softwareelements, class elements or task elements, processes, functions,properties, procedures, sub-routines, segments of a program code,drivers, firmware, micro-codes, circuits, data, database, datastructures, tables, arrays, and parameters. The elements and functionsprovided by the “unit” or “module” may be either combined into a smallernumber of elements, “unit”, or “module” or divided into a larger numberof elements, “unit”, or “module”. Moreover, the elements and “units” or“modules” may be implemented to reproduce one or more CPUs within adevice or a security multimedia card.

Hereinafter, an embodiment of the present disclosure will be describedin detail with reference to the accompanying drawings. Further, indescribing embodiments of the present disclosure, a detailed descriptionof known functions or configurations incorporated herein will be omittedwhen it may make the subject matter of the present disclosureunnecessarily unclear. The terms which will be described below are termsdefined in consideration of the functions in the present disclosure, andmay be different according to users, intentions of the users, orcustoms. Therefore, the definitions of the terms should be made based onthe contents throughout the specification.

Further, the detailed description of embodiments of the presentdisclosure is mainly directed to an OFDM-based communication system,particularly 3GPP EUTRA standard, but the subject matter of the presentdisclosure may be applied to other communication systems having similartechnical backgrounds and channel types through a slight modificationwithout departing from the scope of embodiments of the presentdisclosure, which can be determined by those skilled in the art.

A reference signal is a signal that is used for measuring the state ofchannels between an eNB and users in a wireless mobile communicationsystem, such as a strength or distortion of a channel, a strength of aninterference, a Gaussian noise, or the like, so as to help thedemodulation and decoding of a received data symbol. Another use of thereference signal is to measure the state of a wireless channel. Areceiver may determine the state of a wireless channel between thereceiver and a transmitter by measuring the reception strength of areference signal that is received via the wireless channel after beingtransmitted from the transmitter at an agreed transmission power. Thestate of a wireless channel determined as described above may be used todetermine the data rate which the receiver will request from thetransmitter.

In the recent 3rd evolved wireless mobile communication system standard,such as 3GPP LTE(-A), IEEE 802.16m, or the like, a multi-access schemeusing multiple subcarriers, such as OFDM(A) (orthogonal frequencydivision multiplexing (multi-access)), is employed mostly. In the caseof the wireless mobile communication system that uses the multi-accessscheme using the multiple subcarriers, the performance of channelestimation and measurement may vary based on the number of time symbolsand subcarriers that the reference signal occupies on the time andfrequency axes. Furthermore, the performance of channel estimation andmeasurement may be affected by an amount of power that is allocated tothe reference signal. Therefore, as an amount of wireless resources,such as time, frequency, power, or the like, that is allocated to thereference signal becomes larger, the performance of channel estimationand measurement may become higher. Accordingly, the performance ofdemodulating and decoding a received data symbol may be also improvedand the accuracy of a channel state measurement may be increased.

However, in the case of a general mobile communication system, an amountof wireless resources, such as time, frequency, transmission power, orthe like, is limited, and thus, when a large amount of wirelessresources is allocated to the reference signal, an amount of wirelessresources allocable to a data signal may be relatively decreased. Forthe above reasons, the amount of wireless resources to be allocated tothe reference signal may be appropriately determined by taking intoconsideration the system throughput. Particularly, when Multiple InputMultiple Output (MIMO) is applied, which executes transmission andreception using a plurality of antennas, allocating and measuring areference signal is a significantly important technical item.

At the time of forming a transmission beam pattern, such a MIMO systemmay transmit a precoder matrix indicator (PMI) indicating a precodingwhich optimizes performance of a system, using channel information ofthe receiver obtained by the reference signal. According to whether thereceiver transmits the PMI information, the MIMO system may be dividedinto a closed-loop MIMO system or an open-loop MEMO system.

In case of the closed-loop MIMO system, a UE identifies channelinformation using the reference signal and thus identifies acharacteristic of a corresponding channel. The closed-loop MIMO systemchooses optimal precoding among precoder sets supported by a currentwireless channel, by using the channel state, obtains optimal precoding,and transmits the optimal precoding to an eNB through the PMI. Inaddition, assuming a current wireless channel on an assumption thatderived a precoding is used, the closed-loop MIMO system obtains amaximum data transmission rate and feeds back the maximum datatransmission rate to the eNB through a channel quality indicator (CQI).The eNB having received the feedback may communicate with the UE using aproper transmission/reception precoding, on the basis of correspondinginformation.

In case of the open-loop MIMO system, unlike the closed-loop MIMOsystem, the transmitter and receiver may predetermine and use aprecoding used according to time and frequency resources, instead oftransferring the PMI information to the transmitter by the receiver. Inthis case, the receiver receives the reference signal through acorresponding precoding, transfers a quality of the wireless channel tothe transmitter, using a result of the reception, through the CQI, likethe closed-loop MIMO system. The eNB having received the CQI determinesa scheme in which the UE communicates, on the basis of correspondinginformation.

Generally, the closed-loop MIMO may adaptively utilize channelinformation. Thus the closed-loop MIMO is known to show greater systemperformance than the open-loop MIMO. However, this requires additionaloverhead like a PMI, a loss of performance caused by dynamicinterference in which a beam pattern of an interference signal rapidlychanges according to time may be occurred in a situation where a movingspeed of the UE is very fast or a channel rapidly changes.

Meanwhile, in the case of the open-loop MIMO system, performanceefficiency of the system itself is less than the closed-loop MIMO systembut the open-loop MIMO system is affected less by dynamic interferenceand incurs less feedback overhead for such as a PMI.

As stated earlier, since both the closed-loop MIMO and the open-loopMIMO have respective advantages, recent third-generation evolutionwireless mobile communication system standards such as 3GPP LTE(-A) orIEEE 802.16m support and enable selective use of the closed-loop MIMOand the open-loop MIMO. However, in a system like full dimension-MIMO(FD-MIMO) having multiple transmission antennas and operating aplurality of reference signals, each of the reference signals canselectively operate the closed-loop MIMO system or the open-loop MIMOsystem, respectively. In a channel state measurement method using aplurality of reference signals to enable a UE to effectively measurewireless channel state information, a technology and an apparatus usinga hybrid MIMO system proposed by embodiments of the present disclosuremay use a pre-defined PMI to operate some of a plurality of referencesignals in an open-loop MIMO system and may find an optimum PMI andtransfer the found PMI to an eNB through an uplink control channel, inorder to operate the other reference signals in a closed-loop MIMOsystem. Also, CQI information indicating a UE-supportable datatransmission rate generated on an assumption that precodings ofhorizontal and vertical directions are applied at the same time bycombining a pre-determined PMI corresponding to the open-loop MIMOsystem and the optimal PMI may also be transferred to the eNB throughthe uplink control channel.

The FD-MIMO system refers to a wireless communication system thattransmits data by utilizing several tens or more transmission antennas.

FIG. 1 illustrates a FD-MIMO system according to an embodiment of thedisclosure.

Referring to FIG. 1, a transmission apparatus of an eNB 100 may includedozens or more transmission antennas and transmit a wireless signalusing one or more antennas among the transmission antennas. A pluralityof transmission antennas are placed to maintain the minimum distancefrom each other, as in a case of identification number 110. An exampleof the minimum distance is half of the wavelength of a wireless signalwhich is transmitted. Generally, when the distance corresponding to halfof the wavelength of the wireless signal is maintained between thetransmission antennas, a signal transmitted from each transmissionantenna may be affected by a wireless channel having a low correlation.For example, if a band of a wireless signal transmitted is 2 GHz, thedistance is 7.5 cm, and if the band of a wireless signal transmitted ishigher than 2 GHz, the distance may be further shortened.

In FIG. 1, the dozens or more transmission antennas placed in the eNB100 may be used to transmit a signal to one or a plurality of UEs withat least one between identification numbers 120 and 130. In anembodiment, a proper precoding is applied to the plurality oftransmission antennas and thus the plurality of transmission antennasmay simultaneously transmit the signal to the plurality of UEs. In thisinstance, a single UE may receive one or more information streams.Generally, the number of information streams that a single UE mayreceive may be determined based on the number of reception antennas thatthe UE contains, as well as the channel state.

To efficiently embody the FD-MIMO system, a UE may need to accuratelymeasure a channel state and the scale of interference, and may need totransmit effective channel state information to an eNB using themeasurement. The eNB having received the channel state information maydetermine a UE to which the eNB will transmit a signal, using thechannel state information, in relation to downlink transmission, a datarate at which the eNB will perform the transmission, and a precodingscheme which the eNB will apply. The FD-MIMO system has a large numberof transmission antennas, and thus, when the channel state informationtransmission/reception method of the conventional LTE/LTE-A system isapplied, a large amount of control information needs to be transmittedin an uplink, which may cause an uplink overhead.

Time, frequency, and power resources are limited in a mobilecommunication system. Therefore, when an amount of resources allocatedto a reference signal becomes larger, an amount of resources to beallocated to traffic channel (data traffic channel) transmission becomessmaller, and thus, an absolute amount of data transmitted may bereduced. Likewise, when an amount of resources allocated to a referencesignal becomes larger, performance of channel measurement and estimationis improved, but entire system capacity performance may be degradedsince the absolute amount of data transmitted is reduced. Accordingly,to draw an optimized performance from the perspective of the systemthroughput, resources for the reference signal and resources for thesignal used for the traffic channel transmission need to beappropriately distributed.

FIG. 2 illustrates a wireless resource of one subframe and one resourceblock (RB) in an LTE/LTE-A system.

Referring to FIG. 2, a wireless resource includes one sub-frame on atime axis and one RB on a frequency axis. The wireless resource isformed of 12 subcarriers in the frequency domain, and 14 OFDM symbols inthe time domain, and thus, may have a total of 168 unique frequency andtime locations. In LTE/LTE-A, each unique frequency and time location ofFIG. 2 is referred to as a resource element (RE).

Through the wireless resource of FIG. 2, a plurality of different typesof signals may be transmitted as follows.

1. Cell specific Reference Signal (CRS): The CRS is a reference signalperiodically transmitted for all UEs included in one cell, and may beused by a plurality of UEs in common.

2. DeModulation Reference Signal (DMRS): The DMRS is a reference signaltransmitted for a specific UE, and is transmitted only when data istransmitted to a corresponding UE. The DMRS is formed of a total of 8DMRS ports. In LTE/LTE-A, ports from port 7 to port 14 correspond toDMRS ports and ports maintain orthogonality in order to preventgeneration of interference between them by using CDM or FDM.

3. Physical Downlink Shared Channel (PDSCH): The PDSCH is a data channeltransmitted to the downlink, may be used to transmit traffic to a UE bythe eNB, and may be transmitted using a RE in which a reference signalis not transmitted in a data region of FIG. 2.

4. Channel State Information Reference Signal (CSI-RS): a referencesignal which is transmitted to UEs belonging to one cell is used tomeasure a channel state. A plurality of CSI-RSs may be transmitted in asingle cell.

5. Other control channels (PHICH, PCFICH, and PDCCH): control channelsfor provision of control information necessary for reception of a PDSCHby a UE or for transmission of an ACK/NACK for operation of HARQ withrespect to uplink data transmission.

In addition to the signal, the LTE-A system may configure muting so thatUEs in a cell may receive a CSI-RS that is transmitted from another eNBwithout interference. Muting may be applied to a location where theCSI-RS may be transmitted, and generally, the UE may skip thecorresponding wireless resources and receive a traffic signal. In theLTE-A system, muting is also referred to as zero-power CSI-RS. It isapplied to the location of the CSI-RS due to the characteristic ofmuting, since transmission power is not transmitted.

In FIG. 2, a CSI-RS may be transmitted using some of the locationsexpressed as A, B, C, D, E, E, F, G, H, I, and J, based on the number ofantennas that transmit a CSI-RS. Also, muting may be applied to some ofthe locations expressed as A, B, C, D, E, E, F, G, H, I, and J.Particularly, a CSI-RS may be transmitted through 2, 4, and 8 REs, basedon the number of antenna ports that execute transmission. When thenumber of antenna ports is 2, a CSI-RS is transmitted through half of apredetermined pattern in FIG. 2. When the number of antenna ports is 4,a CSI-RS is transmitted through the whole of a predetermined pattern.When the number of antennas is 8, a CSI-RS is transmitted using twopatterns. Conversely, muting is always executed based on a singlepattern. That is, muting may be applied to a plurality of patterns butmay not be applied to some of a single pattern when the location doesnot overlap a CSI-RS. However, when the location of muting and thelocation of a CSI-RS overlap, muting may be applied to some of a singlepattern.

When a CSI-RS is transmitted for two antenna ports, the CSI-RS transmitsa signal of each antenna port in two REs connected in a time axis, andthe signal of each antenna port is classified as an orthogonal code. Inthe case when a CSI-RS is transmitted with respect to four antennaports, two more REs are used in addition to the CSI-RS for two antennaports and the signals for the two antenna ports are additionallytransmitted in the same manner. In the same manner, the transmission ofa CSI-RS associated with 8 antenna ports may be executed.

A reference signal may be transmitted to measure a downlink channelstate in a cellular system. In the case of the LTE-A system of the 3GPP,a UE measures a channel state between an eNB and the UE using a ChannelState Information Reference Signal (CSI-RS) transmitted by the eNB. Inan embodiment, in the measurement of the channel state, several elementsshould be basically considered and the elements may include aninterference amount in a downlink. The amount of interference in adownlink may include an interference signal generated by an antenna thatbelongs to a neighboring eNB, a thermal noise, and the like, which isimportant when a UE determines the channel state of the downlink. Forexample, when an eNB having a single transmission antenna executestransmission with respect to a UE having a single reception antenna, theUE may determine Es/Io by determining, from a reference signal receivedfrom the eNB, energy per symbol that may be received in the downlink andan amount of interference that is to be simultaneously received in thesection where the corresponding symbol is received. The determined Es/Iomay be converted into a data transmission speed or a value equivalentthereto, and may be reported to the eNB in the form of a CQI, so thatthe eNB may determine a data transmission speed to be used when the eNBexecutes downlink transmission with respect to the UE.

In the case of the LTE-A system, the UE feeds back informationassociated with a channel state of a downlink to the eNB so that the eNButilizes the same for downlink scheduling. That is, the UE measures areference signal that the eNB transmits, and feeds back, to the eNB,information extracted from the measured reference signal in a formdefined in the LTE/LTE-A standard. In LTE/LTE-A, information that the UEfeeds back briefly includes the following three types of information.

l Rank Indicator (RI): the number in which a UE may receive spatiallayers in a current channel state.

l Precoder Matrix Indicator (PMI): an indicator to which a UE prefers ina current channel state.

l Channel Quality Indicator (CQI): a maximum data transmission rate inwhich a UE may receive data in a current channel state. The CQI may bereplaced with an SINR, the maximum error correction code rate, amodulation scheme, data rate per frequency, and the like, which may beutilized to be similar with the maximum data rate.

The RI, PMI, and CQI are interrelated. For example, a precoding matrixsupported in LTE/LTE-A may be defined to be different for each rank.Therefore, a PMI value X when an RI is 1 and a PMI value X when an RI is2 may be interpreted to be different. Also, when a UE determines a CQI,the UE assumes that a PMI and X that the UE reports to an eNB areapplied in the eNB. That is, reporting RI_X, PMI_Y, and CQI_Z to the eNBmay be identical to reporting that a data transmission ratecorresponding to CQI_Z is received when a rank is RI_X and precoding isPMI_Y. As described above, when the UE calculates a CQI, the UE assumesa transmission scheme to be executed with respect to the eNB so that theUE may obtain the optimal performance when the UE actually executestransmission using the corresponding transmission scheme.

Generally, when a large number of transmission antennas are used, suchas FD-MIMO, a corresponding CSI-RS needs to be transmitted. For example,when LTE/LTE-A uses 8 transmission antennas, an eNB transmits a CSI-RScorresponding to 8-ports to a UE, so that the UE measures a downlinkchannel state. In this instance, when the eNB transmits a CSI-RScorresponding to 8 ports, the eNB may use wireless resources including 8REs in a single RB, as shown in A and B of FIG. 2. When the CSI-RStransmission scheme of the LTE/LTE-A is applied to FD-MIMO, as manywireless resources as the number of transmission antennas may need to beassigned to the CSI-RS. That is, when 128 transmission antennas areused, the eNB may transmit a CSI-RS using a total of 128 REs in a singleRB. Such a CSI-RS transmission scheme requires excessive wirelessresources, and thus has disadvantages of reducing wireless resourcesrequired for transmitting and receiving wireless data.

The eNB having many transmission antennas, such as FD-MIMO, transmitsCSI-RS with the following method.

-   -   CSI-RS transmission method 1: A method of allocating and        transmitting wireless resources as much as the number of        antennas to a CSI-RS.    -   CSI-RS transmission method 2: A method of dividing a CSI-RS into        a plurality of dimensions and transmitting a divided CSI-RS.    -   CSI-RS transmission method 3: A method of dividing a CSI-RS into        a plurality of dimensions, applying precoding to each of        CSI-RSs, and transmitting a precoded RS.

The CSI-RS transmission method 1 is a method of allocating as manyCSI-RS resources as the number of antennas belonging to a correspondingeNB and identifying of channel state between the eNB and a UE. Themethod has an advantage of accurately identifying informationcorresponding to all antennas, but as the number of antennas increases,the amount of resources required to be allocated also increase. Inaddition, as noted from FIG. 2, since CSI-RS resources are limited, ifthe number of antennas increases, resources for transmitting a CSI-RSproportionately increase and then overhead according to the increase maybe increased.

FIG. 3A illustrates an eNB which transmits a CSI-RS to a UE by using aCSI-RS transmission method 2.

Referring to FIG. 3A, an eNB operating FD-MIMO according to a CSI-RStransmission method 2 may be composed of 32 antennas in total. 16antennas among them (A0, . . . , A3, B0, . . . , B3, C0, . . . , C3, D0,. . . , D3) are arranged at a first angle with respect to a positivedirection of an X axis, the remaining 16 antennas (E0, . . . , E3, F0, .. . , F3, G0, . . . , G3, H0, . . . , H3) may be arranged at a secondangle with respect to the positive direction of an X axis. In anembodiment, the first angle may be 35° to 55° more specifically, it maybe 45°. In an embodiment, the second angle may be −35° to −55° morespecifically, it may be −45°.

An antenna shape in which N/2 antennas and the remaining N/2 antennasamong N number of antennas are arranged at 90° to each other in the sameposition is referred to as XPOL. The XPOL may be used to obtain a largeantenna gain by placing multiple antennas in a small area.

32 antennas of identification number 300 in FIG. 3A are shown as A0, . .. , A3, B0, . . . , B3, C0, . . . , C3, D0, . . . , D3, E0, . . . , E3,F0, . . . , F3, G0, . . . , G3, H0, . . . , H3, respectively. The 32antennas of FIG. 3A may transmit two kinds of CSI-RSs.

First, H-CSI-RS enabling measurement of the horizontal channel state mayinclude the following 8 antenna ports.

-   -   H-CSI-RS port 0: which includes a transmission signal of an        antenna A3.    -   H-CSI-RS port 1: which includes a transmission signal of an        antenna B3.    -   H-CSI-RS port 2: which includes a transmission signal of an        antenna C3.    -   H-CSI-RS port 3: which includes a transmission signal of an        antenna D3.    -   H-CSI-RS port 4: which includes a transmission signal of an        antenna E3.    -   H-CSI-RS port 5: which includes a transmission signal of an        antenna F3.    -   H-CSI-RS port 6: which includes a transmission signal of an        antenna G3.    -   H-CSI-RS port 7: which includes a transmission signal of an        antenna H3.

As described above, generating a single CSI-RS port by aggregating aplurality of antennas indicates antenna virtualization, which isgenerally executed through linear coupling of a plurality of antennas.

In addition, V-CSI-RS enabling measurement of the vertical channel statemay include the following 4 antenna ports.

-   -   V-CSI-RS port 0: which includes a transmission signal of the        antenna A0.    -   V-CSI-RS port 1: which includes a transmission signal of the        antenna A1.    -   V-CSI-RS port 2: which includes a transmission signal of the        antenna A2.    -   V-CSI-RS port 3: which includes a transmission signal of the        antenna A3.

When a plurality of antennas are arranged in two dimensions in M×N(vertical direction×horizontal direction), a channel of FD-MIMO may bemeasured by using N number of CSI-RS ports in the horizontal directionand M number of CSI-RS ports in the vertical direction. That is, whentwo kinds of CSI-RSs are used, channel state information may beidentified by utilizing M+N number of CSI-RS ports, for M×N number oftransmission antennas. Likewise, identifying information on a largernumber of transmission antennas using a fewer number of CSI-RS ports hasan advantage of reducing CSI-RS overhead.

When transmitting a CSI-RS by using a CSI-RS transmission method 2 asdescribed above, overhead for transmitting the CSI-RS and reportingchannel state information is reduced, compared a CSI-RS with CSI-RStransmission method 1. However, exact channel information for an antennain which the CSI-RS is not transmitted cannot be identified, estimationmay be required with a method such as a Kronecker product to bedescribed later.

FIG. 3B illustrates an eNB, which transmits a CSI-RS to a UE by using aCSI-RS transmission method 3.

The 32 antennas in identification number 340 are transmitted as a singletwo-dimensional (2D) CSI-RS, and the 2D CSI-RS that enables measuringthe channel state of all antennas in the horizontal and verticaldirections may be formed of 32 antenna ports shown in the above. Atransmission employing a sequence determined through a cell ID and thelike to each of antenna ports corresponds to CSI-RS transmission method1, and a precoding may be applied to a sequence of transmission method 1in transmission. The method may allocate a wireless resource for eachantenna so that the accuracy of channel information may increase.However, a relatively larger amount of wireless resources is used forcontrol information or data, and thus, it is not efficient from theperspective of resource efficiency, which is a drawback.

Identification numbers 350 and 360 in FIG. 3B are a method for enablingchannel measurement with respect to a plurality of transmission antennasby a UE while allocating relatively fewer wireless resources, eventhough identification numbers 350 and 360 may have relatively lowaccuracy of channel information using a CSI-RS transmission 3. As aCSI-RS transmission method 2 described above, there is a method fordividing a CSI-RS corresponding to an entire antenna port into N numberof dimensions and transmitting a divided CSI-RS, for example, when atransmission antenna of an eNB is arranged in two dimensions as shown inFIG. 1, the method divides the CSI-RS into two dimensions and transmitsthe divided CSI-RS. In this instance, one CSI-RS is operated as aHorizontal CSI-RS that enables measuring channel information in thehorizontal direction, and the other CSI-RS is operated as a VerticalCSI-RS that enables measuring channel information in the verticaldirection. However, it is different from the CSI-RS transmission method2 in that, if only one signal corresponding to one antenna port isincluded in one CSI-RS in a case of the CSI-RS transmission method 2,signals corresponding to a plurality of antenna ports are included inone CSI-RS in a case of a CSI-RS transmission method 3. If arelationship among the plurality of antenna ports is combined by ahorizontal or vertical precoding corresponding to an antenna and then istransmitted through one CSI-RS transmission resource, a UE may identifyinformation on the plurality of antennas of a corresponding CSI-RS atonce. In this instance, an H-CSI-RS that enables measuring of thechannel state in the horizontal direction may be formed of 8 antennaports as follows.

-   -   H-CSI-RS port 0: which is formed by combining A0, A1, A2, and A3        antennas.    -   H-CSI-RS port 1: which is formed by combining B0, B1, B2, and B3        antennas.    -   H-CSI-RS port 2: which is formed by combining C0, C1, C2, and C3        antennas.    -   H-CSI-RS port 3: which is formed by combining D0, D1, D2, and D3        antennas.    -   H-CSI-RS port 4: which is formed by combining E0, E1, E2, and E3        antennas.    -   H-CSI-RS port 5: which is formed by combining F0, F1, F2, and F3        antennas.    -   H-CSI-RS port 6: which is formed by combining G0, G1, G2, and G3        antennas.    -   H-CSI-RS port 7: which is formed by combining H0, H1, H2, and H3        antennas.

Generating a single CSI-RS port by aggregating a plurality of antennasindicates antenna virtualization, which is generally executed throughlinear coupling of a plurality of antennas. Also, a V-CSI-RS thatenables measuring the channel state in the vertical direction may beformed of 4 antenna ports as follows.

-   -   V-CSI-RS port 0: which is formed by combining A0, B0, C0, D0,        E0, F0, G0, and H0 antennas.    -   V-CSI-RS port 1: which is formed by combining A1, B1, C1, D0,        E1, F1, G1, and H1 antennas.    -   V-CSI-RS port 2: which is formed by combining A2, B2, C2, D2,        E2, F2, G2, and H2 antennas.    -   V-CSI-RS port 3: which is formed by combining A3, B3, C3, D3,        E3, F3, G3, and H3 antennas.

When a plurality of antennas are arranged in two dimensions in M×N(vertical direction×horizontal direction), a channel of FD-MIMO may bemeasured by using N number of CSI-RS ports in horizontal direction and Mnumber of CSI-RS ports in vertical direction. That is, when two CSI-RSsare used, channel state information may be recognized using M+N CSI-RSports, for M×N transmission antennas. Likewise, identifying informationon a larger number of transmission antennas using a fewer number ofCSI-RS ports may reduce CSI-RS overhead. Precoding for combining aplurality of antennas into a single CSI-RS port may be a sequence whichis determined through a cell ID, CSI-RS RNTI, a symbol index, a subframeindex, or a frame index. In FIGS. 3A and 3B, the 32 transmissionantennas are allocated to 8 H-CSI-RS ports and 4 V-CSI-RS ports fortransmission, so as to cause a UE to measure a wireless channel of aFD-MIMO system. An H-CSI-RS enables the UE to measure information on ahorizontal angle between the UE and a transmission antenna of an eNB asidentification numbers 320 and 360. On the other hand, a V-CSI-RSenables the UE to measure information on a vertical angle between the UEand the transmission antenna of the eNB as identification numbers 330and 370.

The following abbreviations may be used to explain an embodiment of thepresent disclosure.

-   -   RI_(H): a rank indicator in which a UE reports a rank of a        channel obtained by applying a vertical precoding to 2D-CSI-RS        or a channel obtained by measuring a horizontal CSI-RS        (H-CSI-RS) to an eNB.    -   RI_(V): a rank indicator in which a UE notifies of a rank of a        channel obtained by applying a horizontal precoding to 2D-CSI-RS        or a channel obtained by measuring a vertical CSI-RS (V-CSI-RS)        to an eNB.    -   PMI_(H): a precoding matrix indicator in which a UE reports to        an eNB by obtaining an optimal precoding based on a channel        obtained by applying a horizontal precoding to a 2D-CSI-RS or a        channel obtained by measuring a horizontal CSI-RS (H-CSI-RS).    -   PMI_(V): a precoding matrix indicator that a UE reports to an        eNB by obtaining an optimal precoding based on a channel        obtained by applying a horizontal precoding to a 2D-CSI-RS or a        channel obtained by measuring a vertical CSI-RS (V-CSI-RS).    -   CQI_(H): a transmission rate of UE-supportable data generated on        an assumption that only a horizontal precoding is applied.    -   CQI_(V): a transmission rate of UE-supportable data generated on        an assumption that only a vertical precoding is applied.    -   CQI_(H)V: a transmission rate of UE-supportable data generated        on an assumption that horizontal and vertical precodings are        applied at the same time.

The horizontal channel state information and vertical channel stateinformation described in an embodiment of the present disclosure may bedescribed using general terms, such as channel state information 1 andchannel state information 2, in another embodiment.

On the basis of a transmitted 2D-CSI-RS or a plurality of CSI-RSs asshown in FIG. 3, a UE may notify of a wireless channel of the FD-MIMOsystem to an eNB by transmitting a RI, PMI, and CQI to the eNB.

FIG. 4 illustrates a UE, which transmits RI, PMI, and CQI for a2D-CSI-RS.

Referring to FIG. 4, an arrow in the figure indicates how one kind ofchannel state information is associated with interpreting another kindof channel state information.

That is, terminating the arrow started from an RI_(V) 400 at a PMI_(V)410 means that an interpretation of PMI_(V) is dependent on a value ofthe RI_(V) 400. In FIG. 4, a UE measures a 2D-CSI-RS and then transmitschannel state information such as feedback 1 to an eNB. In addition, theUE obtains channel information corresponding to horizontality by usinginformation on an obtained optimal vertical precoding, obtains a ranksuch as an RI_(H) 430, obtains an optimal precoding PMI_(H) 440corresponding to a horizontal direction, and then transmits channelstate information such as feedback 2 including a CQI_(H) 450 to the eNB.

In an embodiment, at least two among a RI, a PMI, and a CQI areassociated with each other and transmitted. That is, in a case offeedback 1, an RI_(V) 400 indicates a precoding matrix of a rank whichis designated by a PMI_(V) 410 to be transmitted later. In addition,when an eNB transmits a signal to a UE using the rank indicated by theRI_(V) 400, if a precoding matrix of a corresponding rank designated bythe PMI_(V) 410 is applied to the signal transmission, a CQI_(V) 420 mayinclude a data transmission speed which can be received by the UE orcorresponding information.

In an embodiment, in a case of feedback 2 also, at least two among RI,PMI, and CQI are associated with each other and transmitted as is infeedback 1.

FIG. 5 illustrates a UE, which transmits a RI, PMI, and CQI with respectto a plurality of CSI-RSs.

Referring to FIG. 5, a UE measures a V-CSI-RS and then transmits channelstate information such as feedback 1 to an eNB. In addition, the UEmeasures an H-CSI-RS and transmits channel state information such asfeedback 2 to the eNB.

In an embodiment, a RI, a PMI, and a CQI may be associated with eachother and transmitted. That is, in a case of feedback 1, an RI_(V) 500indicates a precoding matrix of a rank which is indicated by a PMI_(V)510 to be transmitted later. In addition, when an eNB transmits a signalto a UE using the rank designated by the RI_(V) 500, if a precodingmatrix of a corresponding rank designated by the PMI_(V) 510 is applied,a CQI_(V) 520 may include data transmission speed which can be receivedby the UE or corresponding information.

In a case of feedback 2 also, RI, PMI, and CQI are associated with eachother and transmitted as is in feedback 1.

The method of configuring, for a plurality of transmission antennas of aFD-MIMO eNB, a 2D-CSI-RS or a plurality of feedbacks to cause a UE toreport channel state information to an eNB as shown in FIG. 4 and FIG. 5may be one channel state information report method for FD-MIMO. In thismethod, additional implementation is not necessary for generating andreporting channel state information for FD-MIMO by a UE. Meanwhile, whenusing a channel state information report method as shown in FIG. 4,performance of the FD-MIMO system is not sufficiently obtained. Thereason why performance of the FD-MIMO system is not sufficientlyobtained is that, as shown in FIG. 4, only the method of configuring a2D-CSI-RS or a plurality of feedbacks to cause a UE to report channelstate information to eNB is insufficient to cause a UE to report a CQIbased on an assumption of precoding in the case of applying FD-MIMO.

In the FD-MIMO system, when a plurality of transmission antennas arearranged in two dimensions as shown in FIG. 3, precoding of both thevertical and horizontal directions is applied to a signal transmitted toa UE. That is, the UE does not receives a signal to which one ofprecodings corresponding to PMI_(H), and PMI_(V) is applied but receivesa signal to which the precodings corresponding to PMI_(H), and PMI_(V)are applied at the same time.

As shown in FIG. 4 and FIG. 5, when only a CQI_(H) and CQI_(V) to whichthe precodings corresponding to PMI_(H) and PMI_(V) are separatelyapplied are reported to an eNB, the eNB cannot receive a CQI to whichprecoding of both the vertical and horizontal directions is applied, andthus should autonomously determine the same. If the eNB randomlydetermines a CQI determination to which both vertical and horizontalprecodings are applied, on the basis of CQIs to which vertical andhorizontal precodings are respectively applied, such a determination maydegrade the system performance.

A definition for how to determine a CQI to which a plurality ofprecodings is applied is necessary. When calculating a CQI to which onlyone precoding is applied, the UE calculates the CQI on an assumptionthat a precoding which is indicated by RI and PMI notified of by the UEitself is applied to a downlink. However, in a case of the CQI_(HV), theUE may calculate the CQI on an assumption that two precodings areapplied to the downlink at the same time. At this time, the UE mayinterpret that two precodings are applied at the same time in variousmethods, and a Kronecker product may be one of such interpretationmethods. The Kronecker product is defined with respect to two matricesas follows.

$\begin{matrix}{{A \otimes B} = \begin{bmatrix}{a_{11}B} & \ldots & {a_{1\; n}B} \\\vdots & \ddots & \vdots \\{a_{m\; 1}B} & \ldots & {a_{mn}B}\end{bmatrix}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

In the equation 1, A and B are replaced by a precoding matrix to whichPMI_(H) and PMI_(V) are indicated, respectively, such that a precodingto which two precodings are applied at the same time can be obtained.When the UE calculates CQI_(HV) 550, the UE calculates a CQI by assumingthat a precoding obtained by applying the equation to a precoding matrixindicated by PMI_(H) and PMI_(V) is applied to a downlink.

In order to obtain a precoding to which two precodings are applied atthat same time, by using the Kronecker product in the equation 1, a UEand an eNB need different operations, depending on the rank reported bythe UE.

A MIMO system may be divided into a closed-loop MIMO system and anopen-loop MIMO system, according to whether PMI information of areceiver is used, when forming a transmission beam pattern.

In a case of the closed-loop MIMO system, the UE identifies informationof a channel by using a CSI-RS, obtains a rank of a correspondingchannel based on the identified information, notifies of the rank to aneNB through an RI. In addition, the UE may select an optimal precodingamong a precoder set corresponding to a determined rank and transfer aPMI corresponding to a selected precoding to the eNB. In addition, theUE feeds back a transmission rate which can be supported by the UE tothe eNB through a CQI, on the basis of a current channel obtained byassuming that the optimal precoding is applied. The eNB having receivedthe feedback, on the basis of corresponding information, designates theUE to use proper transmission/reception precoding for communication.

On the contrary, in a case of the open-loop MIMO system, unlike theclosed-loop MIMO system, a receiver does not transfer PMI information toa transmitter. Instead, when the receiver of the open-loop MIMO systemgenerates a CQI according to time and frequency resources, obtains asupportable transmission rate by assuming a pre-determined precoding bya higher signaling or a specified scheme in a standard using a precodingto be assumed with respect to a corresponding time and frequency space,and transfers the transmission rate to the transmitter through the CQI.The transmitter having received the CQI from the receiver, on the basisof corresponding information, determines a scheme in which the UEcommunicates.

Generally, the closed-loop MIMO may adaptively utilize channelinformation. Thus the closed-loop MIMO is known to show greater systemperformance than the open-loop MIMO. This is because, in a case of theclosed-loop MIMO, there is a process of selecting and notifying of aprecoding which the UE prefers, while, in a case of the open-loop MIMO,since the process is not included, whenever the eNB transmits aprecoding to the UE, it is difficult to apply a precoding which the UEprefers. However, in order to transmit and receive a signal through theclosed-loop MIMO, an additional overhead of transmitting a PMI to theeNB by the UE is required. In addition, when transmitting and receivinga signal by using the closed-loop MIMO, in a situation in which a movingspeed of the UE is very fast or a channel rapidly changes, a beampattern of an interference signal is rapidly changed according to timeand thus a loss of performance, due to a change of the interferencesignal, may occur. Such interference is referred to as dynamicinterference.

Meanwhile, in the case of the open-loop MIMO system, performanceefficiency of the system itself is lower than the closed-loop MIMOsystem but the open-loop MIMO system has low effect of dynamicinterference and low feedback overhead for such as a PMI. The feedbackoverhead for a PMI is especially importantly affected in FD-MIMO inwhich the number of antennas of the eNB is increased. This is because,the more the transmission antennas of the eNB, the more the number ofbits configuring a PMI for notification of preferred precoding by a UE.

An embodiment of the present disclosure may be based on an assumptionthat a precoding corresponding to the open-loop MIMO are designatedtogether with corresponding rank-related information and the precodingand the information are shared by the eNB and the UE. Accordingly, theUE notifies of an RI with respect to a channel corresponding to theclosed-loop MIMO to the eNB through an uplink control signal, and theeNB may identify a rank of a corresponding precoding based on thenotification.

As mentioned above, a CSI-RS may be operated in various methods in theFD-MIMO system. The method for operating a CSI-RS includes a method forallocating the CSI-RS to all antennas and enabling the UE to measure aplurality of CSI-RSs capable of effectively measuring a large number oftransmission antennas in order to reduce use of wireless resources.

When a 2D-CSI-RS is allocated to all antennas, the 2D-CSI-RS maygenerate a 1D channel by applying a 1D precoding to a channel having aplurality of dimensions. When enabling the UE to measure a plurality ofCSI-RSs, each CSI-RS may be used to measure a channel state with respectto one of the plurality of dimensions for measuring one wirelesschannel. This requires relatively few wireless resources for CSI-RStransmission, compared with allocating a unique CSI-RS port to eachtransmission antennas.

For example, it enables the UE to effectively measure a channel state,by operating two CSI-RSs which are vertical and horizontal for atransmission antenna of the FD-MIMO system arranged in a rectangularshape.

An embodiment of the present disclosure proposes a selective operationof each CSI-RS for one or more of the closed-loop MIMO system and theopen-loop MIMO system in a system such as FD-MIMO having multipletransmission antennas and operating a 2D-CSI-RS or a plurality ofCSI-RSs.

In addition, in a channel state measurement method using a 2D-CSI-RS ora plurality of CSI-RSs to enable a UE to effectively measure wirelesschannel state information, a technology and an apparatus using a hybridMIMO system proposed by embodiments of the present disclosure may use apre-defined PMI to operate a 1D channel derived based on some of 1Dchannels which are based on a 2D-CSI-RS or a plurality of CSI-RSs in anopen-loop MIMO system and may find an optimum PMI and transfer the foundPMI to an eNB through an uplink control channel, in order to operate theother CSI-RSs in a closed-loop MIMO system. Also, CQI_(HV) indicating aUE-supportable data transmission rate generated on an assumption that apre-determined precoding corresponding to the open-loop MIMO system andan optimal precoding corresponding to the closed-loop MIMO system areapplied at the same time, may also be transferred to the eNB through theuplink control channel. In the entire present disclosure, such a MIMOtransmission/reception method may be referred to as Hybrid MIMO.

In a system such as FD-MIMO operating a 2D-CSI-RS or a plurality ofCSI-RSs and supporting a Hybrid MIMO system, an eNB may notify a UE ofwhether to operate each CSI-RS in the open-loop or the closed-loop,using at least one of the following methods.

-   -   Method 1 for defining a CSI-RS operated in an open-loop MIMO        system: when the number of CSI-RS port in one dimension is 1, a        dimension corresponding to a corresponding CSI-RS (vertical or        horizontal) is operated in an open-loop. The number of ports of        a CSI-RS may be changed according to an embodiment, but if the        number of specific CSI-RSs is a pre-determined value, a feedback        method in a dimension corresponding to a corresponding CSI-RS        may be determined    -   Method 2 for defining a CSI-RS operated in an open-loop MIMO        system: when PMI/RI reporting has not been configured in a        corresponding CSI-RS, a dimension corresponding to the        corresponding CSI-RS (vertical or horizontal) is operated in an        open-loop.    -   Method 3 for defining a CSI-RS operated in an open-loop MIMO        system: whether to operate in an open-loop or a closed-loop in a        corresponding CSI-RS is configured using a higher signaling and        it operates in an open-loop or a closed-loop according to the        configuration.

In a case of method 2 for defining a CSI-RS operated in an open-loopMIMO system, a mode of operating without transmitting a PMI and an RImay be set by an eNB in transmission modes 8, 9, and 10 in Rel. 10 LTEsystem, and when using the mode, each of dimensions may be configured toeffectively operate in an open-loop system or a closed-loop system.

As mentioned above, in a communication system using a Hybrid MIMOsystem, a UE feeds back only an RI and a CQI for a precoding in a stateof operating for an open-loop MIMO system. A method of definingprecoding operating in the open-loop MIMO system may include at leastone method of the following methods.

-   -   Method 1 for defining precoding operated in an open-loop MIMO        system: which defines one precoding according to time and        frequency resources.    -   Method 2 for defining precoding operated in an open-loop MIMO        system: which defines a plurality of precodings as a set        according to time and frequency resources.

Basically, the methods 1 and 2 for defining precoding operated in anopen-loop MIMO system are the same for operating by transmitting aCQI_(HV) indicating a UE-supportable data transmission rate generated onan assumption that precodings operated in the closed-loop MIMO and theopen-loop MIMO system are applied at the same time. However, a procedurefor determining open-loop precoding used in a CQI_(HV) may be changed,according to a method for deriving an optimal precoding applied to aUE-supportable data transmission CQI_(HV) and a PMI has transferred aprecoding in which an eNB operate in the closed-loop MIMO transmitted bya UE. In an embodiment, when performing an operation according to method1 for defining precoding operated in an open-loop MIMO system, precodingmay be defined according to time and frequency resources as follows.

-   -   Method 1 for defining one precoding according to a resource:        which allocates precoding corresponding to a PMI_(H) to an        open-loop MIMO and defines the precoding corresponding to a        PMI_(H) according to time and frequency resources.    -   Method 2 for defining one precoding according to a resource:        which allocates precoding corresponding to a PMI_(V) to an        open-loop MIMO and defines the precoding corresponding to a        PMI_(V) according to time and frequency resources.

FIG. 6 illustrates precoding corresponding to a PMI_(H) according to anembodiment, which is allocated to an open-loop MIMO and is definedaccording to time and frequency resources. More specifically, accordingto method 1 for defining one precoding according to a resource, whenprecoding corresponding to a PMI_(H) 640, 690 used in time and frequencyresources is defined based on an open-loop MIMO system assumption, a UEobtains an optimal precoding on the assumption of, accordingly,transmitting a PMI_(V) 610, 660 corresponding to a closed-loop MIMOsystem assumption and a CQI_(HV) 620, 670 which is a maximum datatransmission rate of a composite channel to an eNB is illustrated.

In FIG. 6, a UE feedback refers to information included in a signaltransmitted to an eNB by a UE, and the assumption refers to information,which is not transmitted to an eNB by a UE and is recognized by both theeNB and the UE through definitions made in advance.

In FIG. 6, the UE assumes that the UE receives a 2D-CSI-RS or twoCSI-RSs (a V-CSI-RS and an H-CSI-RS). The 2D-CSI-RS is a CSI-RS fortransmitting by allocating a wireless resource to all antennas, and theV-CSI-RS and the H-CSI-RS are CSI-RSs transmitted to provide otherinformation with respect to a two dimensional antenna arrangementconstituting FD-MIMO. A technology proposed by an embodiment of thepresent disclosure may include a process in which a UE generates channelstate information for a two dimensional antenna arrangement using a2D-CSI-RS or a plurality of CSI-RSs and notifies of the channel stateinformation to an eNB.

In an embodiment, a UE generates vertical channel state information 600,610, 620, etc. and notifies of the vertical channel state information toan eNB. However, the UE may not separately generate horizontal channelstate information and may not notify of the horizontal channel stateinformation to the eNB.

The UE may not separately generate horizontal channel state information.In an embodiment, the UE may determine the horizontal channel stateinformation on the basis of information notified through highersignaling to the UE by the eNB or a rule promised between the eNB andthe UE.

For example, the UE may not generate a horizontal PMI and not notify ofthe horizontal PMI to the eNB. Instead, the UE may assume that verticalprecoding indicated by a PMI_(V) 610 notified of by the UE to the eNBand precoding 640 pre-configured by the eNB are applied to a horizontaldirection, and determine CQI_(HV) 620 based on the assumption.

In an embodiment, the UE obtains a rank of a vertical channel obtainedby applying a pre-determined horizontal precoding or a channel obtainedby measuring a vertical CSI-RS (V-CSI-RS), and notifies of the obtainedrank information to the eNB through an RIV 600.

In an embodiment, it may be assumed that an RI_(H) 630 which is a rankof a channel for a horizontal CSI-RS (H-CSI-RS) is shared between theeNB and the UE through a higher signaling and pre-defined between the UEand the eNB.

After notification of RI_(V) 600, in order to determine an optimalprecoding, the UE may derive two channel state information and use acombination thereof, based on a 2D-CSI-RS or two CSI-RSs, as shown inFIGS. 4 and 5. The UE transfers an optimal precoding through a PMI_(V)610, based on a result derived by combining available precodingcorresponding to the RI_(V) 600, precoding corresponding to an RI_(H)630 and a PMI_(H)(0) 640 pre-defined in the open-loop MIMO systemthrough a channel combined based on a 2D-CSI-RS or a plurality ofCSI-RSs. In an embodiment, the eNB may identify a PMI_(H)(0) on thebasis or a received PMI_(V) 610.

At this time, a PMI_(H)(0) 640 corresponding to a pre-determinedprecoding operated in the open-loop MIMO system is not notified ofthrough an uplink control channel. In contrast, in the case of a CQIindicating a maximum data transmission rate, a maximum data transmissionrate CQI_(HV) 620 obtained through a channel derived on an assumption ofa PMI_(V) 610 derived through a CSI-RS and a pre-defined PMI_(H)(0) 640is notified of to the eNB. In an embodiment, it is illustrated thathorizontal precoding assumed by a UE is changed according to a change ofa time resource. Thus, a precoding assumed by a UE according to a timeresource can be changed and also a precoding assumed by a UE accordingto a frequency resource can be changed.

The UE notifies the eNB of an RIV 650 for the next time and frequencyresources, as for previous time and frequency resources, and assumesthat an RI_(H) 680 is shared through a higher signaling or ispre-defined between the UE and the eNB, as for previous time andfrequency resources. The UE transfers an optimal precoding through aPMI_(V) 660, on the basis of a result derived by combining a precodingcorresponding to a pre-defined RI_(H) 680 and PMI_(H) (1) 690 andavailable precodings corresponding to the RI_(V) 650.

At this time, the UE does not notify of a PMI_(H) (1) 690 correspondingto precoding pre-defined for the next time and frequency resourcesthrough an uplink control channel, as identification number 630, butnotifies of a maximum data transmission rate CQI_(HV) 670 obtainedthrough a channel derived on an assumption of a PMI_(V) 660 derivedthrough a CSI-RS and a pre-defined PMI_(H) (1) 690 to the eNB.

FIG. 7 illustrates precoding corresponding to PMI_(H) according to anembodiment, which is allocated to an open-loop MIMO and is definedaccording to time and frequency resources. More specifically, in FIG. 7,according to method 2 for defining one precoding according to aresource, when precoding corresponding to a PMI_(H) 740, 790 used intime and frequency resources is defined based on an open-loop MIMOsystem assumption, a UE obtains an optimal precoding on the assumptionof, accordingly, transmitting a PMI_(V) 710, 760 corresponding to aclosed-loop MIMO system assumption and CQI_(HV) 720, 770 which is amaximum data transmission rate of a composite channel to an eNB isillustrated.

In an embodiment, as shown in FIG. 6, a UE feedback refers to signalstransmitted to an eNB by a UE, and the assumption refers to a signal,which is not transmitted to an eNB by a UE and is recognized by both theeNB and the UE through definitions made in advance.

In FIG. 7, contrary to FIG. 6, the UE obtains a rank of a channelobtained by applying a vertical precoding to a 2D-CSI-RS or a channelobtained by measuring a horizontal CSI-RS (H-CSI-RS), and notifies ofthe obtained rank to the eNB through RI_(H) 700. It may be assumed thatan RI_(V) 730 which is a rank of a channel with respect to a verticalCSI-RS (V-CSI-RS) is shared between the eNB and the UE through a highersignaling and pre-defined between the UE and the eNB.

After notification of RI_(H) 700, in order to determine an optimalprecoding, the UE may derive two channel state information and use acombination thereof, based on a 2D-CSI-RS or two CSI-RSs, as shown inFIGS. 4 to 6.

The UE transfers an optimal precoding through PMI_(H) 710, based on aresult derived by combining available precoding corresponding to anRI_(H) 700, precoding corresponding to an RI_(V) 730 and a PMI_(V)(0)740 pre-defined in the open-loop MIMO system through a channel combinedbased on a 2D-CSI-RS or a plurality of CSI-RS s.

At this time, a PMI_(V)(0) 740 corresponding to a pre-determinedprecoding operated in the open-loop MIMO system is not notified ofthrough an uplink control channel. In contrast, in the case of a CQIindicating a maximum data transmission rate, a maximum data transmissionrate CQI_(HV) 720 obtained through a channel derived on an assumption ofa PMI_(V) 710 derived through a CSI-RS and a pre-defined PMI_(H)(0) 740is notified of to the eNB.

The UE notifies the eNB of an RI_(H) 750 for the next time and frequencyresources, as for previous time and frequency resources, and may assumethat an RI_(V) 780 is shared through a higher signaling or pre-definedbetween the UE and the eNB, as for previous time and frequencyresources. The UE transfers an optimal precoding through a PMI_(H) 760,on the basis of a result derived by combining a precoding correspondingto a pre-defined RI_(V) 780 and PMI_(V) (1) 790 and available precodingscorresponding to PMI_(H) 760.

At this time, the UE does not notify of a PMI_(V)(1) 790 correspondingto precoding pre-defined for the next time and frequency resourcesthrough an uplink control channel, as identification number 730, butnotifies of a maximum data transmission rate CQI_(HV) 770 obtainedthrough a channel derived on an assumption of a PMI_(H) 760 derivedthrough a CSI-RS and a pre-defined PMI_(HV)(1) 790 to the eNB.

When operated according to method 2 for defining precoding operated inan open-loop MIMO system, according to time and frequency resourcesbased on a 2D-CSI-RS or a plurality of CSI-RSs, it may be assumed that aset of a plurality of precodings is defined based on an open-loop MIMOsystem assumption.

At this time, the UE obtains one optimal precoding set among thepre-defined plurality of precoding sets, assumes PMIs of {PMI_(H),PMI_(V)} corresponding to the obtained precoding set, and transmits aPMI and a CQI_(HV) corresponding to a closed-loop MIMO system assumptionto the eNB. In method 2 for defining precoding operated in an open-loopMIMO system, the UE selects PMIs corresponding to an optimal precodingset among a plurality of precoding sets pre-defined as the following andtransfers one of the PMIs to the eNB. The eNB receives notification ofone PMI from the UE and operates in a hybrid MIMO system analogizingprecoding corresponding to a whole set from a received PMI and using theprecoding.

Method 1 for defining a precoding set according to a resource: totransfer an RI_(V) and a PMI_(V) to an eNB.

Method 2 for defining a precoding set according to a resource: totransfer an RI_(H) and a PMI_(H) to an eNB.

FIG. 8 illustrates a UE, which transfers an RIV and a PMI_(V) to an eNBaccording to method 1 for defining a precoding set according to aresource, according to an embodiment.

Referring to FIG. 8, a UE feedback refers to signals transmitted to aneNB by a UE, and the assumption refers to a signal, which is nottransmitted to an eNB by a UE and is recognized by both the eNB and theUE through definitions made in advance.

In an embodiment, it is assumed that an RI_(V) 830 which is a rank of achannel with respect to a vertical CSI-RS (V-CSI-RS) is shared through ahigher signaling and is pre-defined. As shown in FIG. 6 to FIG. 7, theUE obtains a rank of a channel obtained by measuring a horizontal CSI-RS(H-CSI-RS) or a channel obtained by using a precoding set correspondingto a precoding corresponding to a pre-defined RI_(V) 830, 880 andnotifies of the rank to the eNB through RI_(H) 800. After notificationof RI_(H) 800, in order to derive a PMI, the UE may derive two channelstate information and use a combination thereof, based on a 2D-CSI-RS ortwo CSI-RSs, as described above.

In an embodiment, the UE derives a precoding set {PMI_(H), PMI_(V)(2)}showing an optimal performance, by considering a pre-defined set ofprecodings corresponding to an RI_(V) 830 and an RI_(H) 800 in anopen-loop MIMO system, through a channel combined based on a 2D-CSI-RSand or a plurality of CSI-RSs (identification number 840). The UEtransfers precoding corresponding to an H-CSI-RS of a derived result toan eNB through a PMI_(H) 810. In addition, in a case of a CQI indicatinga maximum data transmission rate, the UE notifies of a maximum datatransmission rate CQI_(HV) 820 obtained through a channel derived byassuming the optimal precoding set {PMI_(H), PMI_(V)(2)} determinedthrough a channel state to the eNB.

The eNB may identify a rank of each of precodings through an RI_(H) 800transmitted by the UE and a pre-defined RI_(V) 830, and identify aprecoding set {PMI_(H), PMI_(V)(2)} corresponding to corresponding timeand frequency resources through a received PMI_(H) 810. The eNBidentifies that a received maximum data transmission rate CQI_(HV) 820is obtained based on an assumption of a precoding set {PMI_(H),PMI_(V)(2)}, by using the information.

For the next time and frequency resources, also, the UE assumes that anRI_(V) 880 which is a rank of a channel with respect to a verticalCSI-RS (V-CSI-RS) is shared between the eNB and the UE through a highersignaling, and pre-defined between the UE and the eNB.

After notification of RI_(H) 880, in order to derive a PMI, the UE mayderive two channel state information and use a combination thereof,based on two CSI-RSs, as described above. The UE derives a precoding set{PMI_(H), PMI_(V)(5)} 890 showing an optimal performance, by consideringa pre-defined set of precodings corresponding to an RI_(V) 880 and anRI_(H) 850 in an open-loop MIMO system, through a channel combined basedon a plurality of CSI-RSs. The UE transfers precoding corresponding toan H-CSI-RS of a derived result to an eNB through a PMI_(H) 860.

In a case of a CQI indicating a maximum data transmission rate, the UEnotifies of a maximum data transmission rate CQI_(HV) 870 obtainedthrough a channel derived by assuming the optimal precoding set{PMI_(H), PMI_(V)(5)} determined through a channel state to the eNB.

The eNB may identify a rank of each of precodings through an RI_(H) 850transmitted by the UE and a pre-defined RI_(V) 880, and identify aprecoding set {PMI_(H), PMI_(V)(5)} corresponding to corresponding timeand frequency resources through a received PMI_(H) 860. The eNBidentifies that a received maximum data transmission rate CQI_(HV) 880is formed by assuming a precoding set {PMI_(H), PMI_(V)(5)}, by usingthe information.

FIG. 9 illustrates a UE, which transfers an RIV and a PMI_(V) to an eNB,using method 2 for defining a precoding set according to a resourcedepending on an embodiment.

Referring to FIG. 9, a UE feedback refers to signals transmitted to aneNB by a UE, and the assumption refers to a signal, which is nottransmitted to an eNB by a UE and is recognized by both the eNB and theUE through definitions made in advance.

In an embodiment, it is assumed that an RI_(H) 930 which is a rank of achannel with respect to a horizontal CSI-RS (H-CSI-RS) may be sharedbetween the eNB and the UE through a higher signaling and pre-definedbetween the UE and the eNB. The UE obtains a rank of a channel obtainedby applying a pre-defined horizontal precoding to 2D-CSI-RS or a channelobtained by measuring a vertical CSI-RS (V-CSI-RS), and notifies of therank to the eNB through an RI_(H) 900. After notification of RI_(H) 900,in order to derive a PMI, the UE may derive two channel stateinformation and use a combination thereof, based on two CSI-RSs, asdescribed above.

The UE derives a precoding set {PMI_(H)(1), PMI_(V)} 940 showing anoptimal performance, by considering a pre-defined set of precodingscorresponding to an RI_(H) 930 and an RI_(V) 900 in an open-loop MIMOsystem, through a channel combined based on a 2D-CSI-RS and or aplurality of CSI-RSs.

The UE transfers precoding corresponding to a V-CSI-RS of a derivedresult to an eNB through a PMI_(V) 910 in an embodiment. In a case of aCQI indicating a maximum data transmission rate, the UE notifies of amaximum data transmission rate CQI_(HV) 920 obtained through a channelderived by assuming the optimal precoding set {PMI_(H)(1), PMI_(V)} 940determined through a channel state to the eNB.

The eNB may identify a rank of each of precodings through an RI_(V) 900transmitted by the UE and a pre-defined RI_(H) 930, and identify aprecoding set {PMI_(H)(1), PMI_(V)} 910 corresponding to correspondingtime and frequency resources through a received PMI_(V) 910. The eNBidentifies that a received maximum data transmission rate CQI_(HV) 920is formed by assuming a precoding set {PMI_(H)(1), PMI_(V)} 940, byusing the information.

For the next time and frequency resources, the UE assumes that an RI_(H)980 which is a rank of a channel with respect to a horizontal CSI-RS(H-CSI-RS) is shared between the eNB and the UE through a highersignaling, and pre-defined between the UE and the eNB.

After notification of RI_(V) 950, the UE may use two channel stateinformation, in order to derive a PMI, by deriving and combining the twochannel state information on the basis of a 2D-CSI-RS or two CSI-RSs asdescribed above. In an embodiment, the UE derives a precoding set{PMI_(H) (0), PMI_(V)} 990 showing an optimal performance, byconsidering a set of precodings corresponding to a pre-defined RI_(H)980 and RI_(V) 950 in an open-loop MIMO system, through a channelcombined based on a 2D-CSI-RS and or a plurality of CSI-RSs. The UEtransfers precoding corresponding to a V-CSI-RS of a derived result toan eNB through a PMI_(V) 960. In an embodiment, in a case of a CQIindicating a maximum data transmission rate, the UE notifies of amaximum data transmission rate CQI_(HV) 970 obtained through a channelderived by assuming the optimal precoding set {PMI_(H)(0), PMI_(V)} 990determined through a channel state to the eNB.

The eNB may identify a rank of each of precodings through an RIV 950transmitted by the UE and a pre-defined RI_(H) 980, and identify aprecoding set {PMI_(H)(0), PMI_(V)} 990 corresponding to correspondingtime and frequency resources through a received PMI_(V) 960.

The eNB identifies that a received maximum data transmission rateCQI_(HV) 980 is formed by assuming a precoding set {PMI_(H)(0), PMI_(V)}990, by using the information.

In an embodiment, an operation in an open-loop MIMO system as describedabove requires previous determination of a precoding in which a UE andan eNB operate according to time and frequency resources. Such a methodfor defining precoding according to a resource is as follows.

-   -   Method 1 for defining precoding according to time and frequency        resources: to define by a subband.    -   Method 2 for defining precoding according to time and frequency        resources: to define by a wideband.

When defining by subband as method 1 for defining precoding according totime and frequency resources, it may be defined by a subband as follows.

-   -   Method 1 for defining precoding by a subband: to define a        PMI_(H) in advance.    -   Method 2 for defining precoding by a subband: to define a        PMI_(V) in advance.    -   Method 3 for defining precoding by a subband: to define a        PMI_(H) and a PMI_(V) by a UE in advance.    -   Method 4 for defining precoding by a subband: to define a        PMI_(V) and a PMI_(H) by a UE in advance.    -   Method 5 for defining precoding by a subband: to define a        plurality of PMI sets {PMI_(H), PMI_(V)} in advance.

Defining precoding by a subband is described in an embodiment but, in asimilar structure, precoding may be defined by a resource block (RB).

FIG. 10 illustrates an example of an assumption of method 1 for definingprecoding for each subband by an eNB and two UEs according to anembodiment.

Referring to FIG. 10, a PMI_(H) is pre-defined through method 1 fordefining precoding by a subband.

In an embodiment, when assuming to use a PMI of a 4 bit width, precodingcorresponding to a PMI_(H) (0), . . . , a PMI_(H) (15) may bepre-defined according to time and frequency resources as shown in FIG.10. A PMI_(H) as defined above and one precoding are operated in HybridMIMO, using method 1 for defining precoding according to a resource. Atleast one value among a subband index, a subframe index, C-RNTI mod Nand a cell id which are included in a UE may be used for allocationaccording to a user, and time and frequency resources. In an entireembodiment, for convenience of explanation, even though it is assumedthat a PMI of a 4 bit width is used, it is obvious that a PMI havingother width may be used.

At this time, when allocating a precoding, such as identificationnumbers 1000 and 1010, another UE using neighboring time and frequencyresources may be designed to minimize the amount of signal inferencecaused by each UE on counterpart UEs. In addition, in an open-loop MIMOsystem such as a transmit diversity and a large-delay CDD which are usedin an existing LTE, it is assumed that one UE communicates. However, inorder to support multiple-users in a hybrid MIMO situation as describedin the example, allocating a precoding for multi-user, as shown in FIG.10, is required.

In the example, it is described that two UEs communicate in open-loopMIMO using a PMI_(H) provided by an eNB, but it is similarly applicableto a plurality of more than two UEs. In this case, unlike when two UEscommunicate using multi-user MIMO, when a plurality of UEs operatetogether in a hybrid MIMO system, more carefully designing a precodingdefinition by considering interference which is caused to each other byeach of UEs is required, unlike the existing system. FIG. 11 illustratesan example of an assumption of method 2 for defining a precoding foreach subband by an eNB and two UEs according to an embodiment.

Referring to FIG. 11, a PMI_(V) may be pre-defined using method 2 fordefining a precoding by a subband. When assuming that a PMI of a 4 bitwidth is used, precodings to PMI_(V)(0), PMI_(V)(15) may be pre-definedaccording to time and frequency resources, as shown in FIG. 11. HybridMIMO communication may be used by using method 2 for defining oneprecoding according to a resource and a PMI_(V) as defined above. Atleast one value among a subband index, a subframe index, C-RNTI mod Nand a cell id which are possessed by, a UE may be used for allocationaccording to a user, time, and frequency resources.

At this time, when allocating a precoding, such as identificationnumbers 1100 and 1110, another UE using neighboring time and frequencyresources may be designed to minimize the amount of signal inferencecaused by each UE on counterpart UEs. In addition, in an open-loop MIMOsystem such as a transmit diversity and a large-delay CDD which are usedin an existing LTE, it is assumed that one UE communicates. However, inorder to support multiple-users in a hybrid MIMO situation as describedin the example, allocating a precoding for multi-user is required, asshown in FIG. 11.

In the example, it is described that two UEs communicate in open-loopMIMO using a PMI_(H) provided by an eNB, but it is similarly applicableto a plurality of more than two UEs. In this case, unlike when two UEscommunicates using multi-user MIMO, when a plurality of UEs operatetogether in a hybrid MIMO system, more carefully designing a precodingdefinition by considering interference which is caused by each UE on oneanother is required, unlike the existing system.

FIG. 12 illustrates an example of an assumption of method 3 for defininga precoding for each subband by an eNB and two UEs according to anembodiment.

Referring to FIG. 12, a PMI_(H) and a PMI_(V) may be pre-defined usingmethod for defining a precoding by a subband. When assuming the use of aPMI of a 4 bit width, precodings corresponding to a PMI_(H) (0), . . . ,a PMI_(H) (15), a PMI_(V) (0), . . . , a PMI_(V) (15) may be pre-definedaccording to time and frequency resources, as shown in FIG. 12. HybridMIMO communication may be used by respectively using methods 1 and 2 fordefining one precoding according to a resource and a PMI_(H) and PMI_(V)as defined above for each UE. As in definition methods 1 and 2, variousvalues such as a subband index, a subframe index, C-RNTI mod N, and acell id, which are included in a UE, may be used for allocationaccording to a user, time, and frequency resources.

In the case of method 3 for defining a precoding by a subband, UE0 usesPMI_(H) for an open-loop MIMO system and UE1 uses a PMI_(V) for anopen-loop MIMO system, so as to minimize the interference caused to eachother by the precodings allocated to PMI_(H) and PMI_(V). In addition,as described above, in an open-loop MIMO system such as transmitdiversity and a large-delay CDD which are used in an existing LTE, it isassumed that one UE communicates. However, in order to supportmultiple-users in a hybrid MIMO situation as described in the example,allocating a precoding for multi-user, as shown in FIG. 12, is required.In the example, it is illustrated that two UEs communicate in open-loopMIMO using a PMI_(H) and PMI_(V) provided by an eNB, but it is similarlyapplicable to a plurality of more than two UEs. In this case, unlikewhen two UEs communicate using multi-user MIMO, when a plurality of UEsoperate together in a hybrid MIMO system, more carefully designing aprecoding definition by considering interference, which is caused byeach UE on one another is required, unlike the existing system.

FIG. 13 illustrates an example of an assumption of method 4 for defininga precoding for each subband by an eNB and two UEs according to anembodiment.

Referring to FIG. 13, a PMI_(V) and PMI_(H) may be pre-defined usingmethod 4 for defining a precoding by a subband. When assuming the use ofa PMI of a 4 bit width, precodings corresponding to a PMI_(H) (0), . . ., a PMI_(H) (15), a PMI_(V) (0), . . . , a PMI_(V) (15) may bepre-defined according to time and frequency resources, as shown in FIG.13. Hybrid MIMO communication may be used by respectively using methods1 and 2 for defining one precoding according to a resource and a PMI_(H)and PMI_(V) as defined above for each UE. As definition methods 1 and 2,various values such as a subband index, a subframe index, C-RNTI mod N,and a cell id, which are included in a UE, may be used for allocationaccording to a user, time, and frequency resources. In the case ofmethod 4 for defining a precoding by a subband, UE0 uses PMI_(V) for anopen-loop MIMO system and UE1 uses a PMI_(H) for an open-loop MIMOsystem, so as to minimize the interference caused to each other by theprecodings allocated to PMI_(H) and PMI_(V). In addition, as describedabove, in an open-loop MIMO system such as a transmit diversity and alarge-delay CDD which are used in an existing LTE, it is assumed thatone UE communicates. However, in order to support multiple-users in asituation of hybrid MIMO as described in the example, allocating aprecoding for multi-user, as shown in FIG. 13, is required. In theexample, it is described that two UEs communicate in open-loop MIMOusing a PMI_(H) and PMI_(V) provided by an eNB, but it is similarlyapplicable to a plurality of more than two UEs. In this case, unlikewhen two UEs communicates using multi-user MIMO, when a plurality of UEsoperate together in a hybrid MIMO system, more carefully designing aprecoding definition by considering interference, which is caused byeach UE on one another, is required, unlike the existing system.

FIG. 14 illustrates an example of pre-defining time and frequencyresources for defining a plurality of precoding sets {PMI_(H), PMI_(V)},using method 5 for defining a precoding by a subband according to anembodiment.

Referring to FIG. 14, when time and frequency resources are allocated inorder to apply method 3 for defining a precoding by a subband, aprecoding set {PMI_(H), PMI_(V)} may be defined for each time andfrequency resource, as shown in Table 1 bellow.

Table 1 indicates a precoding set {PMI_(H), PMI_(V)} definition by asubband.

TABLE 1 freq. time 0 1 2 3 . . . 0 {PMI_(H)(0), PMI_(V)(0)} {PMI_(H)(0),PMI_(V)(1)} {PMI_(H)(0), PMI_(V)(2)} {PMI_(H)(0), PMI_(V)(3)} . . .{PMI_(H)(1), PMI_(V)(1)} {PMI_(H)(1), PMI_(V)(2)} {PMI_(H)(1),PMI_(V)(3)} {PMI_(H)(1), PMI_(V)(0)} {PMI_(H)(2), PMI_(V)(2)}{PMI_(H)(2), PMI_(V)(3)} {PMI_(H)(2), PMI_(V)(0)} {PMI_(H)(2),PMI_(V)(1)} {PMI_(H)(3), PMI_(V)(3)} {PMI_(H)(3), PMI_(V)(0)}{PMI_(H)(3), PMI_(V)(1)} {PMI_(H)(3), PMI_(V)(2)} 1 {PMI_(H)(0),PMI_(V)(1)} {PMI_(H)(0), PMI_(V)(2)} {PMI_(H)(0), PMI_(V)(3)}{PMI_(H)(0), PMI_(V)(0)} . . . {PMI_(H)(1), PMI_(V)(2)} {PMI_(H)(1),PMI_(V)(3)} {PMI_(H)(1), PMI_(V)(0)} {PMI_(H)(1), PMI_(V)(1)}{PMI_(H)(2), PMI_(V)(3)} {PMI_(H)(2), PMI_(V)(0)} {PMI_(H)(2),PMI_(V)(1)} {PMI_(H)(2), PMI_(V)(2)} {PMI_(H)(3), PMI_(V)(0)}{PMI_(H)(3), PMI_(V)(1)} {PMI_(H)(3), PMI_(V)(2)} {PMI_(H)(3),PMI_(V)(3)} 2 {PMI_(H)(0), PMI_(V)(2)} {PMI_(H)(0), PMI_(V)(3)}{PMI_(H)(0), PMI_(V)(0)} {PMI_(H)(0), PMI_(V)(1)} . . . {PMI_(H)(1),PMI_(V)(3)} {PMI_(H)(1), PMI_(V)(0)} {PMI_(H)(1), PMI_(V)(1)}{PMI_(H)(1), PMI_(V)(2)} {PMI_(H)(2), PMI_(V)(0)} {PMI_(H)(2),PMI_(V)(1)} {PMI_(H)(2), PMI_(V)(2)} {PMI_(H)(2), PMI_(V)(3)}{PMI_(H)(3), PMI_(V)(1)} {PMI_(H)(3), PMI_(V)(2)} {PMI_(H)(3),PMI_(V)(3)} {PMI_(H)(3), PMI_(V)(0)} 3 {PMI_(H)(0), PMI_(V)(3)}{PMI_(H)(0), PMI_(V)(0)} {PMI_(H)(0), PMI_(V)(1)} {PMI_(H)(0),PMI_(V)(2)} . . . {PMI_(H)(1), PMI_(V)(0)} {PMI_(H)(1), PMI_(V)(1)}{PMI_(H)(1), PMI_(V)(2)} {PMI_(H)(1), PMI_(V)(3)} {PMI_(H)(2),PMI_(V)(1)} {PMI_(H)(2), PMI_(V)(2)} {PMI_(H)(2), PMI_(V)(3)}{PMI_(H)(2), PMI_(V)(0)} {PMI_(H)(3), PMI_(V)(2)} {PMI_(H)(3),PMI_(V)(3)} {PMI_(H)(3), PMI_(V)(0)} {PMI_(H)(3), PMI_(V)(1)} . . . . .. . . . . . . . . .

Table 1 above is a definition of number of cases with respect toavailable precoding set {PMI_(H), PMI_(V)} for each time and frequencyresource of a UE allocated to an eNB. When assuming the use of a PMI ofa 4 bit width, precoding sets corresponding to {PMI_(H)(0), PMI_(V)(0)},{PMI_(H)(1), PMI_(V)(0)}, {PMI_(H)(15), PMI_(V)(14)}, {PMI_(H)(15),PMI_(V)(15)} may be pre-defined according to appointed time andfrequency resources, as shown in FIG. 14. Hybrid MIMO communication maybe used by respectively using methods 1 and 2 for defining a precodingset according to a resource and a precoding set {PMI_(H), PMI_(V)} asdefined above for each UE. In an embodiment, a combination of {PMI_(H),PMI_(V)} in each resource region indicated in Table 1 may be differentlyapplied according to an embodiment.

Similar to the previous embodiment, the combination of {PMI_(H),PMI_(V)} may be allocated based on at least one value among a subbandindex, a subframe index, C-RNTI mod N, and a cell id, which are includedin a UE, for allocation according to a user, time, and frequencyresources. In the case of method 5 for defining a precoding by asubband, each of UEs combines a precoding set with a 2D-CSI-RS orreference signals H-CSI-RS and V-CSI-RS, using at least one methodbetween methods 1 and 2 for defining a precoding set according to aresource as descried above, using a pre-defined precoding set, derivesan optimal precoding set, and transfers a rank of a channelcorresponding to a precoding of a derived precoding set and an optimalprecoding to an eNB through at least one of a RI and a PMI.

The eNB identifies a precoding set pre-defined based on informationreceived from a UE, identifies a precoding set corresponding to thereceived PMI, and identifies the precoding considered to determineCQI_(HV) as the maximum data transmission rate in which both 2D-CSI-RSor H-CSI-RS and V-CSI-RS are taken into consideration.

In addition, as an example above, in order to support multiple-users bypre-defining a precoding set in a situation of hybrid MIMO, it may beconsidered that a precoding set defined in table 1 is allocated for eachuser.

According to an embodiment, when allocating a precoding by a wideband asin method 2 for allocating a precoding according to time and frequencyresources, a precoding allocation method may be defined using at leastone method of the following methods.

-   -   Method 1 for defining a precoding by a wideband: to define a        PMI_(H) in advance.    -   Method 2 for defining a precoding by a wideband: to define a        PMI_(V) in advance.    -   Method 3 for defining a precoding by a wideband: to define a        PMI_(H) and a PMI_(V) by a UE in advance.    -   Method 4 for defining a precoding by a wideband: to define a        PMI_(V) and a PMI_(H) by a UE in advance.    -   Method 5 for defining a precoding by a wideband: to define a        precoding set {PMI_(H), PMI_(V)} in advance.

FIG. 15 illustrates a method for pre-defining a PMI_(H) for each timeand frequency resource, according to method 1 for defining a precodingby a wideband to each UE according to an embodiment.

Referring to FIG. 15, a PMI_(H) may be pre-defined using method 1 fordefining precoding by a wideband.

In an embodiment, when assuming the use of a PMI of a 4 bit width,precoding corresponding to a PMI_(H) (0), . . . , a PMI_(H) (15) may bepre-defined according to time and frequency resources as shown in FIG.15. Hybrid MIMO communication may be used by using method 1 for definingone precoding according to a resource and a PMI_(H) as defined above. Atleast one value among a subband index, a subframe index, C-RNTI mod Nand a cell id which are included in a UE may be used for allocationaccording to a user, time, and frequency resources.

At this time, when allocating a precoding, such as identificationnumbers 1500 and 1510, another UE using neighboring time and frequencyresources may be designed to minimize the amount of signal inferencecaused by each UE on counterpart UEs. In addition, in an open-loop MIMOsystem such as a transmit diversity and a large-delay CDD which are usedin an existing LTE, it is assumed that one UE communicates. However, inorder to support multiple-users in a hybrid MIMO situation as describedin the example, allocating a precoding for multi-user, as shown in FIG.15, is required. In the example, it is illustrated that two UEscommunicate in open-loop MIMO using a PMI_(H) provided by an eNB, but itis similarly applicable to a plurality of more than two UEs. In thiscase, unlike when two UEs communicate using multi-user MIMO, when aplurality of UEs operate together in a hybrid MIMO system, morecarefully designing a precoding definition by considering interferencecaused by each UE on one another is required, unlike the existingsystem.

FIG. 16 illustrates a method for pre-defining a PMI_(V) for each timeand frequency resource, according to method 2 for defining a precodingby a wideband to each UE according to an embodiment.

Referring to FIG. 16, a PMI_(V) may be pre-defined using method 2 fordefining precoding by a wideband, in an embodiment.

In an embodiment, when assuming the use of a PMI of a 4 bit width,precoding corresponding to a PMI_(H) (0), . . . , a PMI_(H) (15) may bepre-defined according to time and frequency resources as shown in FIG.16. Hybrid MIMO communication may be used by using method 2 for definingone precoding according to a resource and a PMI_(V) as defined above. Atleast one value among a subband index, a subframe index, C-RNTI mod Nand a cell id which are included in a UE may be used for allocationaccording to a user, time, and frequency resources.

At this time, when allocating a precoding, such as identificationnumbers 1600 and 1610, another UE using neighboring time and frequencyresources may be designed to minimize an amount of signal inferencewhich is caused by each UE on counterpart UEs.

In addition, in an open-loop MIMO system such as a transmit diversityand a large-delay CDD which are used in an existing LTE, it is assumedthat one UE communicates. However, in order to support multiple-users ina hybrid MIMO situation as described in the example, allocating aprecoding for multi-user, as shown in FIG. 16, is required. In theexample, it is illustrated that two UEs communicate in open-loop MIMOusing a PMI_(V) provided by an eNB, but it is similarly applicable to aplurality of more than two UEs. In this case, unlike when two UEscommunicate using multi-user MIMO, when a plurality of UEs operatetogether in a hybrid MIMO system, more carefully designing a precodingdefinition by considering interference caused by each UE on one anotheris required, unlike the existing system.

FIG. 17 illustrates a method for pre-defining a PMI_(H) and a PMI_(V)for each UE, according to method 3 for defining a precoding by awideband to each UE according to an embodiment.

Referring to FIG. 17, a PMI_(H) and a PMI_(V) may be pre-defined usingmethod 3 for defining precoding by a wideband.

When assuming the use of a PMI of a 4 bit width, precodingscorresponding to a PMI_(H) (0), . . . , a PMI_(H) (15) may bepre-defined according to time and frequency resources, as shown in FIG.17. Hybrid MIMO communication may be used by respectively using methods1 and 2 for defining one precoding according to a resource and a PMI_(H)and PMI_(V) as defined above for each UE. As definition methods 1 and 2,various values such as a subband index, a subframe index, C-RNTI mod N,and a cell id, which are included in a UE, may be used for allocationaccording to a user, time, and frequency resources. In the case ofmethod 3 for defining a precoding by a wideband, UE0 uses PMI_(H) for anopen-loop MIMO system and UE1 uses a PMI_(V) for an open-loop MIMOsystem, so as to minimize the interference caused to each other by theprecodings allocated to PMI_(H) and PMI_(V).

In addition, similar to the previous embodiment, in an open-loop MIMOsystem such as a transmit diversity and a large-delay CDD which are usedin an existing LTE, it is assumed that one UE communicates. However, inorder to support multiple-users in a hybrid MIMO situation as describedin the example, allocating a precoding for multi-user, as shown in FIG.17, is required. In the example, it is described that two UEscommunicate in open-loop MIMO using a PMI_(H) and PMI_(V) provided by aneNB, but it is similarly applicable to a plurality of more than two UEs.In this case, unlike when two UEs communicate using multi-user MIMO,when a plurality of UEs operate together in a hybrid MIMO system, morecarefully designing a precoding definition by considering interferencecaused by each UE on one another is required, unlike the existingsystem.

FIG. 18 illustrates a method for pre-defining a PMI_(V) and a PMI_(H)for each UE, according to method 4 for defining a precoding by awideband to each UE according to an embodiment.

Referring to FIG. 18, a PMI_(V) and PMI_(H) may be pre-defined usingmethod 4 for defining precoding by a wideband.

When assuming the use of a PMI of a 4 bit width, precodingscorresponding to a PMI_(H) (0), . . . , a PMI_(H) (15), a PMI_(V)(0), .. . , a PMI_(V)(15) may be pre-defined according to time and frequencyresources, as shown in FIG. 18. Hybrid MIMO communication may be used byrespectively using methods 1 and 2 for defining one precoding accordingto a resource and a PMI_(H) and PMI_(V) as defined above for each UE. Asin definition methods 1 and 2, at least one value among a subband index,a subframe index, C-RNTI mod N, and a cell id, which are included in aUE, may be used for allocation according to a user, time, and frequencyresources.

In the case of method 4 for defining a precoding by a wideband, UE0 usesPMI_(V) for an open-loop MIMO system and UE1 uses a PMI_(H) for anopen-loop MIMO system, so as to minimize the interference caused to eachother by the precodings allocated to PMI_(H) and PMI_(V). In addition,similar to the previous embodiment, in an open-loop MIMO system such asa transmit diversity and a large-delay CDD which are used in an existingLTE, it is assumed that one UE communicates. However, in order tosupport multiple-users in a hybrid MIMO situation as described in theexample, allocating a precoding for multi-user, as shown in FIG. 18, isrequired. In the example, it is illustrated that two UEs communicate inopen-loop MIMO using a PMI_(H) and PMI_(V) provided by an eNB, but it issimilarly applicable to a plurality of more than two UEs. In this case,unlike when two UEs communicates using multi-user MIMO, when a pluralityof UEs operate together in a hybrid MIMO system, more carefullydesigning a precoding definition by considering interference caused byeach UE on one another is required, unlike the existing system.

FIG. 19 illustrates an example of pre-defining time and frequencyresources for defining a plurality of precoding sets {PMI_(H), PMI_(V)},using method 5 for defining a precoding by a wideband according to anembodiment.

Referring to FIG. 19, when time and frequency resources are allocated inorder to apply method 3 for defining a precoding by a wideband, aprecoding set {PMI_(H), PMI_(V)} may be defined for each time andfrequency resource, as shown in Table 2 bellow.

Table 2 indicates a precoding set {PMI_(H), PMI_(V)} definition by awideband

TABLE 2 time 0 1 2 3 . . . Precoding set {PMI_(H)(0), PMIV(0)}{PMI_(H)(0), PMI_(V)(1)} {PMI_(H)(0), PMI_(V)(2)} {PMI_(H)(0),PMI_(V)(3)} . . . {PMI_(H)(1), PMIV(1)} {PMI_(H)(1), PMI_(V)(2)}{PMI_(H)(1), PMI_(V)(3)} {PMI_(H)(1), PMI_(V)(0)} {PMI_(H)(2), PMIV(2)}{PMI_(H)(2), PMI_(V)(3)} {PMI_(H)(2), PMI_(V)(0)} {PMI_(H)(2),PMI_(V)(1)} {PMI_(H)(3), PMIV(3)} {PMI_(H)(3), PMI_(V)(0)} {PMI_(H)(3),PMI_(V)(1)} {PMI_(H)(3), PMI_(V)(2)}

Table 2 above defines a number of cases with respect to availableprecoding set {PMI_(H), PMI_(V)} for each time and frequency resource ofa UE allocated to an eNB. Table 2 above indicates an example of aprecoding set {PMI_(H), PMI_(V)} combination according to an embodiment,and a precoding set {PMI_(H), PMI_(V)} may be variously determinedaccording to an embodiment.

When assuming the use of a PMI of a 4 bit width, precoding setscorresponding to {PMI_(H)(0), PMI_(V)(0)}, {PMI_(H)(1), PMI_(V)(0)},{PMI_(H)(15), PMI_(V)(14)}, {PMI_(H)(15), PMI_(V)(15)} may bepre-defined according to time and frequency resources appointed in FIG.19. Hybrid MIMO communication may be used by respectively using methods1 and 2 for defining a precoding set according to a resource and aprecoding set {PMI_(H), PMI_(V)} as defined above for each UE. Similarto the previous embodiment, at least one value among a subband index, asubframe index, C-RNTI mod N, and a cell id, which are included in a UE,may be used for allocation according to a user, time, and frequencyresources. In the case of method 5 for defining a precoding by asubband, each of UEs combines a precoding set with a 2D-CSI-RS orreference signals H-CSI-RS and V-CSI-RS, using at least one methodbetween methods 1 and 2 for defining a precoding set according to aresource as descried above, using a pre-defined precoding set, derivesan optimal precoding set, and transfers a rank of a channelcorresponding to a precoding of a derived precoding set and an optimalprecoding to an eNB through at least one of a RI and a PMI.

The eNB receives the at least one of RI and PMI, identifies a precodingset corresponding to the received PMI by identifying a pre-definedprecoding set, and identifies the precoding considered to determineCQI_(HV) as the maximum data transmission rate in which both 2D-CSI-RSor H-CSI-RS and V-CSI-RS are taken into consideration. In addition, asan example above, in order to support multiple-users by pre-defining aprecoding set in a hybrid MIMO situation, it may be considered that aprecoding set defined in table 2 is allocated for each user.

As mentioned above, an eNB and a plurality of UEs operate in anopen-loop MIMIO system, using pre-defined precodings. At this time, itis necessary to pre-define a precoding for the eNB and plurality of UEs.In an embodiment of the present disclosure, two methods as follows areproposed as a method for defining a precoding according to time andfrequency resources between the eNB and plurality of UEs.

-   -   Method 1 for sharing a precoding definition according to time        and frequency resources: which uses a pre-defined method (a        definition of standards).    -   Method 2 for sharing a precoding definition according to time        and frequency resources: which notifies through a RRC or a L1        signaling by an eNB.

When using a hybrid MIMO system according to method 1 for sharing aprecoding definition according to time and frequency resources, aprecoding is defined by a subband and a wideband, as shown in FIG. 10 toFIG. 19, according to methods 1 and 2 for defining a precoding accordingto time and frequency resources, in standards for a correspondingcommunication. Thus, a corresponding eNB and UE communicates a PMI_(H)and a PMI_(V) in a hybrid MIMO system, using a pre-defined precoding, asshown in FIG. 6 to FIG. 9.

When using a hybrid MIMO system according to method 2 for sharing aprecoding definition according to time and frequency resources, anadditional RRC or L1 signaling is required to define a precoding by asubband and a wideband, as shown in FIG. 10 to FIG. 19, according tomethods 1 and 2 for defining a precoding according to time and frequencyresources. Therefore, a corresponding eNB and UE communicate a PMI_(H)and a PMI_(V) in a hybrid MIMO system, using a pre-defined precoding, asshown in FIG. 6 to FIG. 9.

As shown in FIG. 6 and FIG. 7, when one precoding is defined accordingto time and frequency resources by using a method for defining aprecoding according to a resource, and used in a hybrid MIMO system,methods for selecting an optimal precoding by a closed-loop MIMO system,according to a precoding operated in a pre-defined open-loop MIMOsystem, are as follows.

-   -   Method 1 for selecting a precoding of a closed-loop MIMO system        according to a precoding of an open-loop MIMO system: which        derives an optimal precoding by considering all available        precoder matrices which are pre-defined (through standards).    -   Method 2 for selecting a precoding of a closed-loop MIMO system        according to a precoding of an open-loop MIMO system: which        restricts available types of precodings of a closed-loop MIMO        system according to a precoding of an open-loop MIMO system.

Table 3 indicates a case of selecting an optimal precoding for aclosed-loop MIMO system by considering all available precoder matriceswhich are defined in standards through method 1 for selecting aprecoding of a closed-loop MIMO system according to a precoding of anopen-loop MIMO system.

Table 3 shows a method of considering all available precoding matricesdefined in the standards described below.

TABLE 3 Vertical Horizontal PMI_(V)(0) PMI_(V)(1) PMI_(V)(2) PMI_(V)(3)PMI_(H)(0) ◯ ◯ ◯ ◯ PMI_(H)(1) ◯ ◯ ◯ ◯ PMI_(H)(2) ◯ ◯ ◯ ◯ PMI_(H)(3) ◯ ◯◯ ◯ PMI_(H)(4) ◯ ◯ ◯ ◯ PMI_(H)(5) ◯ ◯ ◯ ◯ PMI_(H)(6) ◯ ◯ ◯ ◯ PMI_(H)(7)◯ ◯ ◯ ◯ PMI_(H)(8) ◯ ◯ ◯ ◯ PMI_(H)(9) ◯ ◯ ◯ ◯ PMI_(H)(10) ◯ ◯ ◯ ◯PMI_(H)(11) ◯ ◯ ◯ ◯ PMI_(H)(12) ◯ ◯ ◯ ◯ PMI_(H)(13) ◯ ◯ ◯ ◯ PMI_(H)(14)◯ ◯ ◯ ◯ PMI_(H)(15) ◯ ◯ ◯ ◯

As described in Table 3, each of a PMI_(H) and a PMI_(V) may consider,with respect to all counterpart PMI_(H) and PMI_(V), accordingly, at thetime of deriving, a wireless channel state may be derived by consideringall counterpart precoder matrices.

Generally, an optimal horizontal precoding for a UE may be changedaccording to the precoding which is a vertical precoding. The presentdisclosure proposes a two-dimensional PMI restriction technique.Generally, a PMI restriction is to restrict the range of a PMI which maybe selected and notified by a UE. When applying the PMI restriction asdescribed above, in a process of selecting an optimal PMI by a UE,searching in a smaller range may decrease complexity of calculation ofthe UE and a PMI overhead of which an eNB is notified by the UE.

In standards according to method 2 for selecting a precoding of aclosed-loop MIMO system according to a precoding of an open-loop MIMOsystem proposed in an embodiment of the present disclosure, a method forrestricting available types of precodings of a closed-loop MIMO systemaccording to a precoding of an open-loop MIMO system includesrestricting a PMI which may be designated in a closed-loop, according toa precoding determined depending on open-loop MIMO.

That is, when assuming a PMI_(V)(0) by a UE, a PMI_(H) may be selectedin PMI values designated for a PMI_(V)(0). In addition, when assuming aPMI_(V)(1), a PMI_(H) may be selected in PMI values designated for aPMI_(V)(1). That is, a range of a selectable PMI_(H) value is restricteddepending on a PMI_(V) value to be assumed by a UE. When applying a PMIrestriction according to an embodiment of the present disclosure, therange of a PMI_(H) selected by a closed-loop MIMO scheme may be changeddepending on a PMI_(V) value determined by open-loop MIMO by a UE.

In standards according to method 2 for selecting a precoding of aclosed-loop MIMO system according to a precoding of an open-loop MIMOsystem, methods for restricting available types of precodings of aclosed-loop MIMO system according to a precoding of an open-loop MIMOsystem include at least one of the following methods.

-   -   Method 1 for restricting available types of precodings of a        closed-loop MIMO system according to a precoding of an open-loop        MIMO system: to restrict according to the case of a PMI_(H) and        a PMI_(V).    -   Method 2 for restricting available types of precodings of a        closed-loop MIMO system according to a precoding of an open-loop        MIMO system: to restrict only a specific PMI_(H).    -   Method 3 for restricting available types of precodings of a        closed-loop MIMO system according to a precoding of an open-loop        MEMO system: to restrict only a specific PMI_(V).

Table 4 indicates restrictions according to the case of a PMI_(H) and aPMI_(V), based on method 1 for selecting a precoding of a closed-loopMIMO system according to a precoding of an open-loop MIMO system.

More particularly, the following Table 4 indicates restrictionsaccording to the case of a PMI_(H) and a PMI_(V).

TABLE 4 Vertical Horizontal PMI_(V)(0) PMI_(V)(1) PMI_(V)(2) PMI_(V)(3)PMI_(H)(0) ◯ X ◯ X PMI_(H)(1) X ◯ ◯ X PMI_(H)(2) X ◯ ◯ ◯ PMI_(H)(3) ◯ ◯X X PMI_(H)(4) ◯ X X X PMI_(H)(5) X X ◯ ◯ PMI_(H)(6) ◯ X X ◯ PMI_(H)(7)◯ ◯ ◯ ◯ PMI_(H)(8) X X X ◯ PMI_(H)(9) X X ◯ ◯ PMI_(H)(10) ◯ ◯ X XPMI_(H)(11) X ◯ ◯ X PMI_(H)(12) ◯ X X ◯ PMI_(H)(13) ◯ ◯ ◯ X PMI_(H)(14)X ◯ ◯ ◯ PMI_(H)(15) ◯ ◯ ◯ ◯

As shown in Table 4, each of a PMI_(H) and PMI_(V) determines whether tobe considered or not when deriving a CQI_(HV) for each of a counterpartPMI_(H) and PMI_(V). In Table 4, a combination for whether to considerwith respect to each of corresponding PMIs may be variously determinedaccording to an embodiment.

In an embodiment, a method of configuring as shown in Table 4 configuresfor all PMI_(H) and PMI_(V) and thus it is advantageous in optimizingeach UE's performance. Meanwhile, when sharing such a pre-definitionthrough standards or receiving such pre-definition through a signal, alot of resources are required.

Table 5 below indicates how to define a precoding set {PMI_(H), PMI_(V)}for operation of methods 1 and 2 for defining a precoding set accordingto a resource, using method 1 for selecting a precoding of a closed-loopMIMO system according to a precoding of an open-loop MIMO system.

More particularly, Table 5 below indicates how to define a precoding set{PMI_(H), PMI_(V)}.

TABLE 5 Vertical Horizontal PMI_(V)(0) PMI_(V)(1) PMI_(V)(2) PMI_(V)(3)PMI_(H)(0) ◯ X X X PMI_(H)(1) X ◯ X X PMI_(H)(2) X X ◯ X PMI_(H)(3) X ◯X X PMI_(H)(4) ◯ X X X PMI_(H)(5) X X ◯ X PMI_(H)(6) X X X ◯ PMI_(H)(7)X X ◯ X PMI_(H)(8) X X X ◯ PMI_(H)(9) X X X ◯ PMI_(H)(10) ◯ X X XPMI_(H)(11) X ◯ X X PMI_(H)(12) X X X ◯ PMI_(H)(13) X X ◯ X PMI_(H)(14)X ◯ X X PMI_(H)(15) X X ◯ X

As shown in Table 5, since each PMI_(H) and PMI_(V) is possible toconsider for only one counterpart PMI_(V) and PMI_(H) even though justone value of PMI_(H) and PMI_(V) is received, it is possible todetermine the precoding considered to configure CQI_(HV) as the maximumpossible data transmission rate by identifying a counterpart value andconsidering all values. In Table 5, a combination for whether toconsider with respect to each of corresponding PMIs may be variouslydetermined according to an embodiment.

In an embodiment, in the case of such a configuration method, since itis possible to identify by finding number of cases even though just onevalue is reported, without assuming feedback for a specific PMI_(H) orPMI_(V), it is possible to flexibly handle according to a situation andactively handle a H-CSI-RS and a V-CIS-RS, and reduce overhead accordingto a PMI report.

Table 6 below indicates restrictions on a specific PMI_(H) according tomethod 2 for restricting available types of precodings of a closed-loopMIMO system according to a precoding of an open-loop MIMO system.

More particularly, Table 6 below indicates how to restrict a specificPMI_(H).

TABLE 6 Vertical Horizontal PMI_(V)(0) PMI_(V)(1) PMI_(V)(2) PMI_(V)(3)PMI_(H)(0) ◯ ◯ ◯ ◯ PMI_(H)(1) ◯ ◯ ◯ ◯ PMI_(H)(2) ◯ ◯ ◯ ◯ PMI_(H)(3) X XX X PMI_(H)(4) ◯ ◯ ◯ ◯ PMI_(H)(5) ◯ ◯ ◯ ◯ PMI_(H)(6) ◯ ◯ ◯ ◯ PMI_(H)(7)◯ ◯ ◯ ◯ PMI_(H)(8) ◯ ◯ ◯ ◯ PMI_(H)(9) ◯ ◯ ◯ ◯ PMI_(H)(10) ◯ ◯ ◯ ◯PMI_(H)(11) ◯ ◯ ◯ ◯ PMI_(H)(12) ◯ ◯ ◯ ◯ PMI_(H)(13) ◯ ◯ ◯ ◯ PMI_(H)(14)◯ ◯ ◯ ◯ PMI_(H)(15) ◯ ◯ ◯ ◯

As shown in Table 6, in method 2 for restricting available types ofprecodings of a closed-loop MIMO system according to a precoding of anopen-loop MIMO system, an eNB configures not to use a specific PMI_(H),and does not consider each PMI_(V) when deriving a CQI_(HV) for aspecific PMI_(H). According to an embodiment, a PMI_(H) which is not tobe used may be variously determined.

Accordingly, according to an embodiment, since such a pre-definition isshared between a UE and an eNB through standards, or only a specificPMI_(H) which is to be excluded at the time of receiving through asignal transmission between the UE and the eNB is shared or transferred,unlike method 1 for restricting available types of precodings of aclosed-loop MIMO system according to a precoding of an open-loop MIMOsystem, restriction is possible even using a relatively smaller downlinkcontrol resource. But, it is not possible to configure a PMI_(H) and aPMI_(V) in more detail compared with method 1 for restricting availabletypes of precodings of a closed-loop MIMO system according to aprecoding of an open-loop MIMO system. Thus, it may be relativelyunfavorable to optimize each performance. In addition, the embodimentrestricts just one PMI_(H), but if necessary, it is possible to restricta plurality of PMI_(H)s.

Table 7 below indicates how to restrict a specific PMI_(V) according tomethod 3 for restricting available types of precodings of a closed-loopMIMO system according to a precoding of an open-loop MIMO system.

More particularly, Table 7 below indicates how to restrict a specificPMI_(V).

TABLE 7 Vertical Horizontal PMI_(V)(0) PMI_(V)(1) PMH_(V)(2) PMI_(V)(3)PMI_(H)(0) ◯ ◯ X ◯ PMI_(H)(1) ◯ ◯ X ◯ PMI_(H)(2) ◯ ◯ X ◯ PMI_(H)(3) ◯ ◯X ◯ PMI_(H)(4) ◯ ◯ X ◯ PMI_(H)(5) ◯ ◯ X ◯ PMI_(H)(6) ◯ ◯ X ◯ PMI_(H)(7)◯ ◯ X ◯ PMI_(H)(8) ◯ ◯ X ◯ PMI_(H)(9) ◯ ◯ X ◯ PMI_(H)(10) ◯ ◯ X ◯PMI_(H)(11) ◯ ◯ X ◯ PMI_(H)(12) ◯ ◯ X ◯ PMI_(H)(13) ◯ ◯ X ◯ PMI_(H)(14)◯ ◯ X ◯ PMI_(H)(15) ◯ ◯ X ◯

As shown in Table 7, in method 3 for restricting available types ofprecodings of a closed-loop MIMO system according to a precoding of anopen-loop MIMO system, an eNB configures not to use a specific PMI_(V),and does not consider each PMI_(H) when deriving a CQI_(HV) for aspecific PMI_(H). According to an embodiment, a PMI_(V) which is not tobe used may be variously determined.

Accordingly, in the pre-definition, since PMI information which is notto be used is shared between a UE and an eNB through standards, or onlya specific PMI_(V) which is to be excluded at the time of receivingthrough a signal transmission between the UE and the eNB is shared ortransferred, unlike method 1 for restricting available types ofprecodings of a closed-loop MIMO system according to a precoding of anopen-loop MIMO system, restriction is possible even using a relativelysmaller downlink control resource. But, it may be difficult to configurea PMI_(H) and a PMI_(V) in more detail compared with method 1 forrestricting available types of precodings of a closed-loop MIMO systemaccording to a precoding of an open-loop MIMO system. In addition, theembodiment restricts just for one PMI_(V) but, if necessary, it ispossible to restrict for a plurality of PMI_(V)s.

According to a situation, at least one method among methods 1, 2, and 3for restricting a precoding of a closed-loop MIMO system according to aprecoding of an open-loop MIMO system may be applied at the same time.It may be assumed that a precoding restriction as shown in table 4 isdefined through standards, by method 1 for restricting a precoding of aclosed-loop MIMO system according to a precoding of an open-loop MIMOsystem. At this time, when assuming that a precoding restriction signalas shown in Table 7 using method 3 for restricting a precoding of aclosed-loop MIMO system according to a precoding of an open-loop MIMOsystem is received through at least one of a RRC, a L1 signaling, and adownlink control signal, a precoding restriction of a closed-loop MIMOsystem according to a precoding of an open-loop MIMO system, which isrecognized by a UE and an eNB, is described in Table 8 below.

More particularly, Table 8 below indicates an example of a method forrestricting a precoding by combining methods 1 and 3 for restricting aprecoding of a closed-loop MIMO system according to a precoding of anopen-loop MIMO system.

TABLE 8 Vertical Horizontal PMI_(V)(0) PMI_(V)(1) PMI_(V)(2) PMI_(V)(3)PMI_(H)(0) ◯ X X X PMI_(H)(1) X ◯ X X PMI_(H)(2) X ◯ X ◯ PMI_(H)(3) ◯ ◯X X PMI_(H)(4) ◯ X X X PMI_(H)(5) X X X ◯ PMI_(H)(6) ◯ X X ◯ PMI_(H)(7)◯ ◯ X ◯ PMI_(H)(8) X X X ◯ PMI_(H)(9) X X X ◯ PMI_(H)(10) ◯ ◯ X XPMI_(H)(11) X ◯ X X PMI_(H)(12) ◯ X X ◯ PMI_(H)(13) ◯ ◯ X X PMI_(H)(14)X ◯ X ◯ PMI_(H)(15) ◯ ◯ X ◯

As shown in Table 8, each of a PMI_(H) and a PMI_(V) is not consideredfor a specific PMI_(V) additionally received as well as Table 5, at thetime of obtaining an optimal precoding and deriving a CQI_(HV), byconsidering both methods 1 and 3 for restricting available types ofprecodings of a closed-loop MIMO system according to a precoding of anopen-loop MIMO system. According to an embodiment, a precodingcombination which is not to be considered may be variously determined.

In this scheme, for a PMI_(H) and a PMI_(V) configured in detail inmethod 1 for restricting available types of precodings of a closed-loopMIMO system according to a precoding of an open-loop MIMO system, aPMI_(H) or a PMI_(V) which are to be excluded when additionallycalculating a CQI_(HV) according to a channel state between a UE and aneNB may be configured.

FIG. 20 illustrates an operation of an eNB using method 1 for definingone precoding according to a resource, according to an embodiment of thepresent disclosure.

Referring to FIG. 20, in step 2000, an eNB transmits, to a UE, at leastone of a reference signal and configuration information related to achannel information report.

In step 2010, an eNB may identify the precoding which is a precodingcorresponding to an RI_(H) and a PMI_(H) pre-defined according to timeand frequency resources in which a UE will receive a CSI-RS. Accordingto an embodiment, step 2010 may be identified by the eNB, without aseparate operation, on the basis of pre-configured information.

In step 2020, the eNB receives an RI_(V) which is a rank of a channelobtained by measuring a vertical CSI-RS (V-CSI-RS) or a channel obtainedby applying a horizontal precoding pre-defined to a 2D-CSI-RS receivedfrom the UE and identifies rank of a corresponding channel, andidentifies by receiving a PMI_(V) and a CQI_(HV).

In step 2030, an eNB determines a maximum data transmission rateCQI_(HV) derived by assuming a pre-defined RI_(H) and PMI_(H) and areceived RI_(V) and PMI_(V) at the same time, transmits a control signalto a UE, according to the determination. In an embodiment, the eNB maydetermine a CQI_(HV) based on at least one piece of informationtransmitted in step 2000. In addition, the eNB may transmit/receive adata signal with a UE, according to the determination.

FIG. 21 illustrates an operation of a UE using method 1 for defining oneprecoding according to a resource, according to an embodiment of thepresent disclosure.

Referring to FIG. 21, in step 2100, a UE may receive, from an eNB, atleast one of a reference signal and configuration information related toa channel information report.

In step 2110, a UE identifies the precoding which is a precodingcorresponding to an RI_(H) and a PMI_(H) pre-defined according to timeand frequency resources in which a CSI-RS will be received. According toan embodiment, step 2110 may be identified by the UE, without a separateoperation, on the basis of pre-configured information.

In step 2120, a UE obtains a rank of a channel obtained by measuring avertical CSI-RS (V-CSI-RS) or a channel obtained by applying apre-defined horizontal precoding to 2D-CSI-RS, and notifies of theobtained rank to an eNB through an RI_(M).

In step 2130, after notification of RI_(V), in order to determine anoptimal precoding, the UE may simultaneously assume a pre-defined RI_(M)and PMI_(H) and a derived RI_(V) and determine an optimal precoding.

In step 2140, the UE obtains a maximum data transmission ratecorresponding to the determined optimal precoding, and transfers themaximum data transmission rate to the eNB through a PMI_(V) and aCQI_(HV).

After, the UE may receive data, from the eNB, based on informationtransferred to the eNB.

FIG. 22 illustrates an operation of an eNB using method 2 for definingone precoding according to a resource, according to an embodiment of thepresent disclosure.

Referring to FIG. 22, in step 2200, an eNB notifies, to a UE, of atleast one of a reference signal and configuration information related toa channel information report.

In step 2210, the eNB may identify the precoding which is a precodingcorresponding to an RI_(V) and a PMI_(V) pre-defined according to timeand frequency resources in which the UE will receive a CSI-RS. Accordingto an embodiment, step 2210 may be identified by the eNB, without aseparate operation, on the basis of pre-configured information.

In step 2220, the eNB receives an RI_(H) which is a rank of a channelobtained by measuring a horizontal CSI-RS (H-CSI-RS) or a channelobtained by applying a vertical precoding pre-defined to a 2D-CSI-RSreceived from the UE and identifies rank of a corresponding channel, andidentifies by receiving a PMI_(H) and a CQI_(HV). In step 2230, the eNBdetermines a maximum data transmission rate CQI_(HV) derived by assuminga pre-defined RI_(V) and PMI_(V) and a received RI_(H) and PMI_(H) atthe same time, transmits a control signal to the UE, according to thedetermination. In an embodiment, the eNB may determine a CQI_(HV) byadditionally considering at least one piece of information transmittedin step 2200. In addition, the eNB may transmit/receive a data signalwith a UE, according to the determination.

FIG. 23 illustrates an operation of a UE using method 2 for defining oneprecoding according to a resource, according to an embodiment of thepresent disclosure.

Referring to FIG. 23, in step 2300, a UE may receive, from an eNB, atleast one of a reference signal and configuration information related toa channel information report.

In step 2310, a UE identifies the precoding which is a precodingcorresponding to an RIV and a PMI_(V) pre-defined according to time andfrequency resources in which a CSI-RS will be received. According to anembodiment, step 2310 may be identified by the UE, without a separateoperation, on the basis of pre-configured information.

In step 2320, the UE obtains a rank of a channel obtained by measuring ahorizontal CSI-RS (H-CSI-RS) or a channel obtained by applying apre-defined vertical precoding to 2D-CSI-RS, and notifies of theobtained rank to an eNB through a RI_(H).

In step 2330, after notification of RI_(H), in order to determine anoptimal precoding, the UE may simultaneously assume a pre-defined RI_(V)and PMI_(V) and a derived RI_(V) and determine an optimal precoding.

In step 2340, the UE obtains a maximum data transmission ratecorresponding to the determined optimal precoding, and transfers themaximum data transmission rate to the eNB through a PMI_(H) and aCQI_(HV).

After, the UE may receive data, from the eNB, based on informationtransferred to the eNB.

FIG. 24 illustrates an operation of an eNB using method 1 for defining aprecoding set according to a resource, according to an embodiment of thepresent disclosure.

Referring to FIG. 24, in step 2400, an eNB notifies, to a UE, at leastone of a reference signal and configuration information related to achannel information report.

In step 2410, the eNB may identify a corresponding precoding set{PMI_(H), PMI_(V)} and a RI_(H) pre-defined according to time andfrequency resources in which the UE will receive a CSI-RS. According toan embodiment, step 2410 may be identified by the eNB, without aseparate operation, on the basis of pre-configured information.

In step 2420, the eNB receives an RI_(V) which is a rank of a channelobtained by measuring a vertical CSI-RS (V-CSI-RS) or a channel obtainedby applying a horizontal precoding pre-defined to a 2D-CSI-RS receivedfrom the UE and identifies the rank of a corresponding channel, andidentifies by receiving a PMI_(V) and a CQI_(HV).

In step 2430, the eNB identifies a pre-defined precoding set {PMI_(H),PMI_(V)} corresponding a received RI_(V) and to a pre-defined RI_(H)through a received PMI_(V).

In step 2440, the eNB determines a maximum data transmission rateCQI_(HV) derived by assuming at least one among an RI_(H), a PMI_(H), anRI_(V), and a PMI_(V) at the same time, transmits a control signal tothe UE, according to the determination. In an embodiment, the eNB maydetermine a CQI_(HV) by additionally considering at least one piece ofinformation transmitted in step 2400. In addition, the eNB maytransmit/receive a data signal with a UE, according to thedetermination.

FIG. 25 illustrates an operation of a UE using method 1 for defining aprecoding set according to a resource, according to an embodiment of thepresent disclosure.

Referring to FIG. 25, in step 2500, a UE may receive, from an eNB, atleast one of a reference signal and configuration information related toa channel information report.

In step 2510, the eNB may identify a corresponding precoding set{PMI_(H), PMI_(y)} and an RI_(H) pre-defined according to time andfrequency resources in which a CSI-RS will be received. According to anembodiment, step 2510 may be identified by the UE, without a separateoperation, on the basis of pre-configured information.

In step 2520, the UE obtains a rank of a channel obtained by measuring avertical CSI-RS (V-CSI-RS) or a channel obtained by applying apre-defined horizontal precoding to 2D-CSI-RS, and notifies of theobtained rank to an eNB through an RI_(V).

In step 2530, after notification of RI_(M), in order to determine anoptimal precoding, the UE may assume a pre-defined precoding set{PMI_(H), PMI_(V)} corresponding to a derived RI_(V) and a pre-definedRI_(H) and determine an optimal precoding.

In step 2540, the UE may transfer, to an eNB, a value corresponding to aPMI_(V) of the optimal precoding set determined as described above.

In step 2550, the UE may obtain a maximum data transmission ratecorresponding to the PMI_(V) and transfer the maximum data transmissionrate to the eNB through a CQI_(HV).

After, the UE may receive data, from the eNB, based on informationtransferred to the eNB.

FIG. 26 illustrates an operation of an eNB using method 2 for defining aprecoding set according to a resource, according to an embodiment of thepresent disclosure.

Referring to FIG. 26, in step 2600, an eNB notifies, to a UE, of atleast one of a reference signal and configuration information related toa channel information report.

In step 2610, the eNB may identify a corresponding precoding set{PMI_(H), PMI_(V)} and an RIV pre-defined according to time andfrequency resources in which the UE will receive a CSI-RS. According toan embodiment, step 2610 may be identified by the eNB, without aseparate operation, on the basis of pre-configured information.

In step 2620, the eNB receives an RI_(H) which is a rank of a channelobtained by measuring a horizontal CSI-RS (H-CSI-RS) or a channelobtained by applying a vertical precoding pre-defined to a 2D-CSI-RSreceived from the UE and identifies rank of a corresponding channel, andidentifies by receiving a PMI_(H) and a CQI_(HV).

In step 2630, the eNB identifies a pre-defined precoding set {PMI_(H),PMI_(V)} corresponding to a received RI_(H) and a pre-defined RI_(V)through a received PMI_(V).

In step 2640, the eNB determines a maximum data transmission rateCQI_(HV) derived by assuming at least one among an RI_(H), a PMI_(H), anRI_(V), and a PMI_(V) at the same time, transmits a control signal tothe UE, according to the determination. In an embodiment, the eNB maydetermine a CQI_(HV) by additionally considering at least one piece ofinformation transmitted in step 2600. In addition, the eNB maytransmit/receive a data signal with a UE, according to thedetermination.

FIG. 27 illustrates an operation of a UE using method 2 for defining aprecoding set according to a resource, according to an embodiment of thepresent disclosure.

Referring to FIG. 27, in step 2700, a UE may receive, from an eNB, atleast one of a reference signal and configuration information related toa channel information report.

In step 2710, the UE may identify a corresponding precoding set{PMI_(H), PMI_(V)} and an RI_(V) pre-defined according to time andfrequency resources in which a CSI-RS will be received or a channelobtained by applying a pre-defined vertical precoding to 2D-CSI-RS.According to an embodiment, step 2710 may be identified by the UE,without a separate operation, on the basis of pre-configuredinformation.

In step 2720, the UE obtains a rank of a channel obtained by measuring ahorizontal CSI-RS (H-CSI-RS) or a channel obtained by applying apre-defined vertical precoding to 2D-CSI-RS, and notifies of theobtained rank to an eNB through a RI_(H).

In step 2730, after notification of RI_(V), in order to determine anoptimal precoding, the UE may assume a pre-defined precoding set{PMI_(H), PMI_(V)} corresponding to a derived RI_(H) and a pre-definedRI_(V) and determine an optimal precoding.

In step 2740, the UE may transfer, to the eNB, a value corresponding toa PMI_(H) of the determined optimal precoding set.

In step 2750, the UE may obtain a maximum data transmission ratecorresponding to the PMI_(H) and transfer the maximum data transmissionrate to the eNB through a CQI_(HV).

FIG. 28 illustrates an equipment drawing of an eNB in a FD-MIMO system,according to an embodiment of the present disclosure.

Referring to FIG. 28, an eNB according to an embodiment may include atleast one of an eNB controller 2800, a transmitter 2810, and a receiver2820. The eNB controller 2800 may control all operations of the eNB anddetermine a value related to an operation of the eNB, on the basis ofinformation which is transmitted and received.

An eNB according to an embodiment may determine how to configure for aplurality of CSI-RSs or a 2D-CSI-RS, using the eNB controller 2800.

According to an embodiment, the eNB controller 2800 may notify of asignal based on the determined result to the UE by controlling atransmitter 2810.

In addition, the eNB controller 2800 may determine how to configurechannel state information to be transmitted by a UE, and notify of thedetermined result to the UE, by controlling the transmitter 2810. Inaddition, the eNB controller 2800 may transmit a 2D-CSI-RS or aplurality of CSI-RSs to the UE by controlling the transmitter 2810.

In addition, in an embodiment, the eNB controller 2800 may configure aCSI-RS of a UE and channel state information, and receive channel stateinformation notified from the UE, by controlling a receiver 2820.

FIG. 29 illustrates an equipment drawing of a UE in a FD-MIMO system,according to an embodiment of the present disclosure.

Referring to FIG. 29, a HE (terminal) according to an embodiment mayinclude at least one of a UE controller 2900, a transmitter 2910, and areceiver 2920. The UE controller 2900 may control all operations of theUE and determine a value related to an operation of the UE, on the basisof information which is transmitted and received.

In an embodiment, the UE controller 2900 may receive, from the eNB,notification of at least one piece of information related to how toconfigure channel state information and report to an eNB andconfiguration information with respect to a plurality of CSI-RSs or a2D-CSI-RS, by controlling a receiver 2920.

The UE controller 2900 may control a reception with respect to aplurality of CSI-RSs or a 2D-CSI-RS of the UE, on the basis of contentsnotified from an eNB.

In addition, the UE controller 2900 may receive a plurality of CSI-RSsby controlling the receiver 2920.

In addition, the UE controller 2900 may generate channel stateinformation generated based on a plurality of received CSI-RSs, andreport, to the eNB, the generated channel state information, bycontrolling a transmitter 2910.

Although exemplary embodiments of the present disclosure have been shownand described in this specification and the drawings, they are used ingeneral sense in order to easily explain technical contents of thepresent disclosure, and to help comprehension of the present disclosure,and are not intended to limit the scope of the present disclosure. It isobvious to those skilled in the art to which the present disclosurepertains that other modified embodiments on the basis of the spirits ofthe present disclosure besides the embodiments disclosed herein can becarried out.

1. A method for transmitting and receiving channel state information bya terminal of a mobile communication system, the method comprising:identifying at least one of first precoding information or first rankinformation corresponding to a first dimension; receiving a referencesignal corresponding to a second dimension from a base station;identifying at least one of second precoding information or second rankinformation corresponding to the second dimension, based on thereference signal; and transmitting, to the base station, channel stateinformation identified based on at least one of the first precodinginformation, the first rank information, the second precodinginformation, or the second rank information.
 2. The method of claim 1,wherein identifying the at least one of the second precoding informationor the second rank information corresponding to the second dimensioncomprises identifying at least one of the second precoding informationor the second rank information corresponding to the second dimension,using the first precoding information and the first rank informationbased on the reference signal and a pre-determined correspondingrelation.
 3. The method of claim 1, wherein identifying the at least oneof the first precoding information or the first rank informationcorresponding to the first dimension comprises identifying at least oneof the first precoding information or the first rank informationcorresponding to the first dimension based on pre-determined informationaccording to time and frequency resources.
 4. The method of claim 1,wherein transmitting the channel state information to the base stationcomprises transmitting, to the base station, channel-related informationwhich has identified according to the first precoding information, thefirst rank information, the second precoding information, and the secondrank information.
 5. A method for transmitting and receiving channelstate information by a base station of a mobile communication system,the method comprising: identifying at least one of first precodinginformation or first rank information corresponding to a firstdimension; transmitting, to a terminal, a reference signal correspondingto a second dimension; and receiving, from the terminal, channel stateinformation identified based on at least one of the first precodinginformation, the first rank information, second precoding information,or second rank information, wherein at least one of the second precodinginformation or the second rank information corresponding to the seconddimension is identified based on the reference signal.
 6. The method ofclaim 5, wherein the second precoding information and the second rankinformation are identified using the first precoding information and thefirst rank information, based on the reference signal and pre-determinedcorresponding relation.
 7. The method of claim 5, wherein the firstprecoding information and the first rank information are identifiedbased on the basis of pre-determined information according to time andfrequency resources, wherein receiving the channel state informationcomprises receiving, from the terminal, channel-related informationwhich has been identified according to the first precoding information,the first rank information, the second precoding information, and thesecond rank information.
 8. A terminal for transmitting and receivingchannel state information in a mobile communication system, the terminalcomprising: a transceiver configured to transmit and receive a signal;and a controller configured to: control the transceiver, identify atleast one of first precoding information or first rank informationcorresponding to a first dimension, receive, from a base station, areference signal corresponding to a second dimension, identify at leastone of second precoding information or second rank informationcorresponding to the second dimension based on the reference signal, andtransmit, to the base station, channel state information identifiedbased on at least one of the first precoding information, the first rankinformation, the second precoding information, or the second rankinformation.
 9. The terminal of claim 8, wherein the controller isfurther configured to identify at least one of the second precodinginformation or the second rank information corresponding to the seconddimension, using the first precoding information and the first rankinformation based on the reference signal and a pre-determinedcorresponding relation.
 10. The terminal of claim 8, wherein thecontroller is further configured to identify at least one of the firstprecoding information or the first rank information corresponding to thefirst dimension based on pre-determined information according to timeand frequency resources.
 11. The terminal of claim 8, wherein thecontroller is further configured to transmit, to the base station,channel-related information identified according to the first precodinginformation, the first rank information, the second precodinginformation, and the second rank information.
 12. An base station fortransmitting and receiving channel state information in a mobilecommunication system, the base station comprising: a transceiverconfigured to transmit and receive a signal; and a controller configuredto control the transceiver, identify at least one of first precodinginformation or first rank information corresponding to a firstdimension, transmit, to a terminal, a reference signal corresponding toa second dimension, and receive, from the terminal, channel stateinformation identified based on at least one of the first precodinginformation, the first rank information, second precoding information,or second rank information, wherein at least one of the second precodinginformation or the second rank information corresponding to the seconddimension is identified based on the reference signal.
 13. The basestation of claim 12, wherein the second precoding information and thesecond rank information are identified using the first precodinginformation and the first rank information based on the reference signaland pre-determined corresponding relation.
 14. The base station of claim12, wherein the first precoding information and the first rankinformation are identified based on pre-determined information accordingto time and frequency resources.
 15. The base station of claim 12,wherein the controller is further configured to receive, from theterminal, channel-related information identified according to the firstprecoding information, the first rank information, the second precodinginformation, and the second rank information.